David Hume

(Knowledge,—its conditions and limits)

The interest with which Hume entered on philosophical studies appears from his correspondence. ' I began to consider seriously how I should proceed in my philosophical enquiries. I found that the moral philosophy, transmitted to us by antiquity, laboured under the same inconvenience that has been found in their natural philosophy, of being entirely hypothetical, and depending more upon invention than experience, . . . without regarding human nature. This, therefore, I resolved to make my principal study, and the source from which I would derive every truth in criticism, as well as in morality.'

At the age of twenty-five, in the retreat he had selected in France, he began philosophical research with the enthusiasm of one who had found his life-work. The title chosen for his work was 'A Treatise of Human Nature : being an attempt to introduce the experimental method of reasoning into moral subjects.' It thus appears that 'the experimental method' was that which allured him to independent study, and which held out the prospect of fresh ' discovery,' even as in physical research. His field of study was 'human nature'; his basis, 'experience'; his method an observational enquiry into the intellectual conditions on which a knowledge of things is acquired by us. His main enquiry, therefore, was concerned with the origin of our thoughts and fancies and feelings as to things around us.

The chief interest to us in Hume's philosophy centres in its distinctive feature, his brave and exclusive reliance on Experience. Its strength and its weakness are to be traced to its root. My purpose is to sketch his system as clearly and carefully as I may find possible within the limits. If I succeed in presenting Hume as he really was in the field of philosophy, my leading purpose will be gained. I shall then be willing to leave to the reader the more extended criticism which seems desirable.

His basis was Experience; this always, this only. What he sought was an interpretation of human nature by reference to our experience, aided by a keen sceptical outlook against assumptions, inventions, and hypotheses. These were the evils which had at all stages involved philosophy in confusion, exposing its systems to ridicule. David J Hume's accepted task was to rid philosophy of these evils, placing before thinking men a simple and complete exposition of human experience, guarded at every point by an unhesitating and bold scepticism as to everything that proposes to go a step beyond Experience. This is the true significance of ' Hume's scepticism.' If the reader keep this description well in view from the first, he will have a fair chance of understanding Hume better than he has commonly been understood in his native land.

A safe and sure basis for philosophy we certainly have in Experience. All knowledge must begin in Experience, and all knowledge must be within Experience. Even thus, however, our difficulties are only beginning. We may speak of the simplicity of Experience, but the conditions of our knowledge are not simple, nor are they easily interpreted. Hume sees this from the outset, saying in the introduction to his Treatise, 'If truth be at all within the reach of human capacity, it is certain it must be very deep and abstruse; and to hope we shall arrive at it without pains, while the greatest geniuses have failed with the utmost pains, must certainly be esteemed sufficiently vain and presumptuous.' It is in fact easy to say, ' we shall keep to experience'; but to set forth all that is involved within ' common experience' is no easy task. Owning this, Hume shut himself off from his ordinary surroundings, and, retreating to France, devoted himself to three years of the closest observation and reflection. It was no light thing he resolved upon, and he was ready for any sacrifice, animated by the expectation that there lay within his reach discoveries which would have permanent value. Expectations are not always fulfilled, but brave resolves are ever to be honoured, and they have ever reward in their execution, — though readers may doubt whether ' experience' sustains this view of life's efforts.

Everyone can see from what directions difficulties must come, when he considers the wide sphere of existence in which we have our place, and the conditions under which we interpret the facts of experience. Hume does not mean that the universe lies within an individual's experience; he only asks how far the universe can be understood by reference to our experience. Hume does not mean that our senses, being essentially like those of the animals, are the measure of reality; he asks what interpretation we put on our impressions by use of our understanding. Accordingly, the entire first volume on his Treatise, extending to 475 pages, is 'of the understanding'; and all through it there run references to 'unknown causes,' and to 'particular causes of particular events,' while he holds that the actual relation between cause and effect never comes within our experience. These few references are enough to shew through what an African thicket the path of exploration must be cut.

He begins with 'the perceptions of the human mind'; the outlook a man has on his surroundings; what is the origin of his 'perceptions'? how does he perceive things? how is he affected by things? The physiology of nerve and brain was unknown when Hume set to work. This field of research was therefore closed to him, though he did much to turn attention in its direction. Witness Reid's Inquiry into the Human Mind, on the Principles of Cotnmon Sense (1763), with his discussion of the organs of sense, and of the impressions made on them, largely suggested by Hume's Treatise.

Hume speaks of perceptions 'entering' the mind, dwelling on the manner in which 'they strike upon the mind' and 'make their way into our thought and consciousness.' These phrases seem almost to suggest that perceptions are made outside, and force their way into an inner consciousness where they are stored. Nothing so crude as this is intended. He is only encountering the disadvantages of popular usage. His defence is given later, when he writes, ' It is very difficult to talk of the operations of the mind with perfect propriety and exactness, because common language has seldom made any very nice distinctions between them' (p. 187).

The historic position was such as to involve philosophical research in needless perplexity. Locke's great essay On the Human Understanding held the field, having run through five editions before Hume entered on his philosophical enquiries. Locke, having first expended his force on a polemic against 'innate ideas,' had insisted that 'all the materials of reason and knowledge' come 'from Experience,' that observation is 'employed either about external sensible objects or about the internal operations of our minds,' that the mind may be regarded as ' white paper void of all characters,' that ideas are the figures 'which the busy and boundless fancy of man has painted on it,' and that 'all ideas come from Sensation and Reflection.' Our Senses 'convey into the mind several distinct perceptions of things,' and Reflection, which is 'the notice the mind takes of its own operations,' 'furnishes the understanding with another set of ideas, which could not be had from things without.' Hume takes Locke's standpoint, acknowledges our dependence on Experience only, and entering with the freshness of youthful enthusiasm into the enquiry as to the origin of our ideas on the conditions implied, he works out his scheme of association under the sway of custom, develops his doctrine of ignorance of matter, of mind, and of causality, presenting a philosophic scepticism as the outcome. In this his grand service is an exposure of the inherent weakness of an empirical philosophy. Locke's Essay was an epoch-making book; Hume's Treatise prepared the way for a new and grander epoch in the history of the science of man. With such tracings the reader may follow readily the unfolding of Hume's ' system,' of which he speaks so confidingly and confidently as the discussion proceeds.

What does Experience mean—your experience and mine? How does there originate out of this simple source all the variety of relations belonging to it? How can we by interpretation of it reach a science of human nature? These are Hume's grand questions. In seeking an answer, he hopes to achieve large discoveries in philosophy. His search is first for the simple elements of our experience,—next for the origin of the strange complexity which it involves,—and ultimately for the philosophy of existence possible to us within its limits. 'The subjects of the understanding and passions make a complete chain of reasoning by themselves'; and beyond these lies 'the examination of morals, politics, and criticism.' These, taken together, give his general survey of the field of research.

The primary element of Experience is Impression. 'This arises in the soul originally, from unknown causes ' (22). 'An impression first strikes upon the senses and makes us perceive heat or cold, thirst or hunger, pleasure or pain of some kind or other ' (22). Under this name are included ' all our sensations, passions, and emotions, as they make their first appearance in the soul' (12). He thus distinguishes between an outer and an inner source of impression. All that can be said as to their rise is that ' they strike upon the mind, and make their way into our thought or consciousness' (12). Impressions 'are all so The bracketed figures refer to the pages of the 1st Ed. (in 3 vols.)

It is clear and evident, that they admit of no controversy' (65). Here is no room for doubt. Our consciousness of impression leaves no place for question or appeal. ' The extent and force of the human understanding ' (4) still lies beyond this, involving wider questions. When Experience is taken in its utmost simplicity, all that can be said is that we are conscious of some feeling ; and ' every one of himself will readily perceive the difference between feeling and thinking' (12). Even at this early stage we are dealing with a set of words of which we have no interpretation, such as ' consciousness,' ' understanding,' 'thought,' 'mind,' 'soul'; but it does not seem possible to make our statements without being allowed their provisional use. Whether these also admit of no controversy is not as yet determined. We have only before us the primary form of ' the perceptions of the human mind,'—impressions coming through the senses or from within our nature itself. But in naming them so, he • would not be understood to express the manner in which our lively perceptions are produced in the soul, but merely the perceptions themselves.' These impressions are fleeting. They ' make their way into consciousness' and then vanish, to be followed by others. Are they then utterly lost as particular feelings, having had only a momentary existence ? Assuredly not. The experience of which they are the primary phase, includes more than this, as a consequence, we may say. ' In thinking and reasoning,' ideas arise in the mind. These are ' the faint images of our sensations, passions, and emotions, as they .make their first appearance in the soul.' In this use of the term ' Idea,' there is a departure from Locke's usage, who took ' Idea' as the term to include all the phenomena in consciousness. In thus departing from Locke's usage, he says—' Perhaps I rather restore the word, idea, to its original sense, from which Mr Locke had perverted it, in making it stand for all our impressions ' (13, note).; What then are these ' Ideas,' and what the conditions of their origin ? How are ' the faint images ' of our impressions produced? They are not fading impressions; they take the place of vanished impressions, which had greater ' force and liveliness' while they lasted. 'Of the impression there is a copy taken by the mind, which remains after the impression ceases; and this we call an idea' (22). Impressions 'are copied by the memory and imagination, and become ideas' (22). This involves divergence from the 'white paper' theory as if nature made an impression on a sensitive surface. The theory suggests an activity of mind in producing a copy; and it is added that the ideal has less 'force and liveliness,' is 'faint and low,' and ' when it entirely loses that vivacity' which characterises impressions, it ' is a perfect idea' (24). Hume does not deal with the question how - the mind makes the copy. He takes it merely as a fact within our experience. Subsequent references throughout his first volume are consistent with those now quoted, but do not add any thing by way of explanation. Under the action of Memory and Imagination, 'an impression again makes its appearance as an idea' (23). Memory 'preserves the original form in which its objects were presented' (25). Ideas are spoken of as 'adequate representations of objects' (58). Somewhat more definite is the reference to the ' judgments of our senses» (89), which, it is admitted, ' undergo correction.' On the other hand, Hume speaks of ' two bodies presenting themselves,' and yet he is careful to repeat—' My philosophy pretends only to explain the nature and causes of our perceptions, or impressions and ideas' (118). While perceptions are said to ' make their way into our thought or consciousness,' he represents this as 'a mere passive admission of the impressions through the organs of sensation' (133).

The next advance is the noting of similarity between Impressions and Ideas. 'The first circumstance that strikes my eye is the great resemblance betwixt our impressions and ideas in every other particular, except their degree of force and vivacity. The one seem to be in a manner the reflection of the other, so that all the perceptions of the mind are double, and appear both as impressions and ideas ' (13). 'This circumstance seems to me remarkable' (14). He dwells upon it with special interest, regarding it as in some sense a ' discovery,' and of the first importance. 'The Ideas I form are exact representations of the impressions I felt'; ' these two species of perception are exactly correspondent' (16); and there is a 'constant conjunction of resembling impressions.' If there is ' a copy taken by the mind,' it seems a natural result that there should be a resemblance. But Hume is arrested by the 'constant conjunction ' of the two things as if it were settled by the nature of the mind that the copy must follow the impression, so that the perceptions of the mind by a provision of nature are invariably double. And we ' find by constant experience, that the simple impressions always take the precedence of their correspondent ideas ' (17). At a later stage we find him repeat his view of the importance of all this. ' No discovery could have been made more happily for deciding all controversies concerning ideas than that above mentioned, that impressions always take the precedency of them, and that every idea with which the imagination is furnished, first makes its appearance in a correspondent impression' (65). The lack of explanation of how the copy is taken proves a serious disadvantage now, even when we grant the doubleness, and the uniformity of sequence, and add that ' all our simple ideas in their first appearance are derived from simple impressions' (16).

But Hume recognises that it becomes needful to distinguish between simple and complex in our perceptions. 'Upon a more accurate survey I find I have been carried away too far by the first appearance, and that I must make use of the distinction of perceptions into simple and complex, to limit this general decision, that all our ideas and impressions are resembling' (14). This leads to a modification of view, shewing how much must depend on the explanation to be given of how the 'copy' is made. 'I observe that many of our complex ideas never had impressions that correspond to them; and that many of our complex impressions never are exactly copied in ideas' (15). For example, the idea we have of the ' New Jerusalem ' or of ' Paris.' He then feels constrained to admit that ' the rule is not universally true, that they are exact copies of each other ' (15). This suggests that nature does not provide for ' double perceptions ' though the phenomena are dual; and that the later phrase, 'judgments of the senses 'is truer to experience than the statement that 'there is a copy of the impression taken by the mind.' Both statements, however, imply an activity of mind somewhat obscured by the references to 'resemblance ' and 'correspondence.' Our author, nevertheless, continues attracted by the 'discovery' of resemblance; and he ' ventures to affirm that the rule holds without exception ' in the case of 'simple perceptions.' 'Every simple impression has a correspondent idea' (15). But even here the suggestion of 'representation,' 'image,' 'copy,' is not easily supported by reference to 'experience.' The idea of red 'is taken as an example, but we find it more difficult to form ' an idea of red,' than an idea of ' a red apple,' and even on this point ideas will differ according as we are more familiar with the Scotch apple or with the American. Hume's modification of his view by reference to complex perceptions, seems to apply even to simple perceptions, so far, at least, as to awaken doubt as to his first position that ' the difference between impressions and ideas consists in the degrees of force and liveliness with which they strike upon the mind' (11).

The complexity of Experience opens out still further. Even impressions must be distinguished as ' those of Sensation and those of Reflexion ' (22). The first kind arises in the soul originally from unknown causes. The second is derived in a great measure from our ideas, and that in -the following order. An impression first strikes upon the senses, and makes us perceive . . . pleasure or pain of some kind or other. Of this impression there is a copy taken by the mind, which remains after the impression ceases. This idea of pleasure or pain, when it returns upon the soul, produces the new impressions of desire and aversion, hope and fear, which may properly be called impressions of reflexion, because derived from it. These again are copied by the memory and imagination, and become ideas; which perhaps in their turn give rise to other impressions and ideas. So that the impressions of reflexion are antecedent to their correspondent ideas, but posterior to the ideas of sensation and derived from them.' This passage is not too long for its purpose, for the complexity described belongs to the common experience, quite apart from philosophy. This double relation of thought to feeling is such that at one time thought depends on feeling; at another, feeling depends on thought. The first feeling comes to us, we know not how ; the second is awakened by our thought. This complexity seems to present to view the whole range of enquiry. Hume is so impressed by it that it leads him even to change the order of investigation so far as to pass ' impressions ' in order to treat of ' ideas.' The inducement is curiously explained. 'As the impressions of reflection, viz., passions, desires and emotions, which principally deserve our attention arise mostly from ideas, it will be necessary to reverse that method which, at first sight, seems most natural; and in order to explain the nature and principles of the human mind, give a particular account of ideas before we proceed to impressions. For this reason I have here chosen to begin with ideas' (23). This is a temptation springing from his ultimate object—' an attempt to introduce the experimental method of reasoning into moral subjects.' But the philosopher who declares that ' the only solid foundation we can give to the science of man must be laid on experience and observation' (6), becomes bound to keep by the natural order of experience, in order to read accurately its testimony. If nature has so ordered our experience that all perceptions are doubly, and those of sense ' always take the precedence of their correspondent ideas,' this deviation from the natural order is a mistake, and is likely to throw the ' system' into confusion. The significance of the complexity is, however, to be seriously considered. It involves a dualism in the history of impressions. There are ' impressions of sensation ' coming from without, which ' strike upon the senses '; and there are impressions from within, ' desires and emotions,' depending on reflection. ' The examination of our sensations belongs more to anatomists and natural philosophers than to moral'(23); but, when 'they make their way into consciousness,' it is quite otherwise, for it remains true that ' all impressions are internal and perishing existences' (339), having their place within us in accordance with conditions of consciousness. After having remarked the ' constant conjunction' of impressions and ideas, and having found in this an order of dependence, inasmuch as we ' find by constant experience that the simple impressions always take the precedence of their correspondent ideas, but never appear in the contrary order' (17), it seems a singular deviation from the natural order to ' give a particular account of ideas before we proceed to impressions ' (23). In consequence the treatment ' of the impressions of the senses and memory' is delayed till Part III., section 5, p. 151. This determination 'to begin with ideas' affects seriously the structure of the Treatise.

The effect on the development of the theory is to present Empiricism in a more trying light. The field of life's activity is illuminated by impressions, external and internal; all ideas are dependent on them; ' innate ideas' are, therefore, excluded (21). Impressions are unaccounted for; they are, however, classified, according to their source, as external or internal; how they arise is unknown to us (a physiology of the senses and of organic sensibilities not being at command). The main difficulties are now full in view,—how have impressions their ' correspondent ideas'; how do these ideas subsist as a system; how are those relations essential to the scheme of knowledge originated and maintained ; and how does this scheme stand related to the system of things we name the universe ? With nothing more than impressions and their copies to work with, a faint outline of the sceptical result is already shining through this description of our experience. Its income pleteness involves its insecurity, and this means doubt. In this study of ' the extent and force of the human understanding,' the theory that mind is as 'white paper, void of all characters' is being discredited ; and the theory that it is as 'a copying-press' does not show to advantage.* We need to ascertain by direct observation 'the force of the human understanding.'

The first question is, How have impressions their ' correspondent ideas' ? To 'give a particular account of ideas, before we proceed to impressions,' is 'to reverse' the natural order. It is to act as the builder who proceeds with the structure before he has made sure of the foundation. To delay the primary question from Part I., section 2, until Part III., section 5, was a serious thing. Let the reader transfer sections 5 and 6 of Part III. to their natural place in Part I., after section 2, and it will appear how brief and insufficient is the treatment, how naturally the author admits that he is employing ' materials which are of a mixed and heterogeneous nature ' (rsr), and consequently how much of the brief discussion falls out of account when it is placed in its natural position.

In proceeding to 'give a particular account of ideas,' the discussion enters into the heart of all the complications connected with their relations. We become concerned with the conditions of reflections; memory and imagination are called into requisition; association of ideas are noted; and forthwith we are drifting out on the wide ocean where single impressions are as difficult to descry as the mountain rills flowing to the sea. Here each voyager has his separate experience. Men originate their own systems of thought. There are associations of impressions and of their 'correspondent ideas' according to similarity and dissimilarity; and of things according to their contiguity in place and in time; and of occurrences according to the relation of cause and effect. We speak of substance and qualities, and modes of existence; and according to the natural activity of reflection we institute a search into space and time, and all problems of existence presented by the great universe.

Hume is eager to grapple with all the complications here involved, and to him is due the honour belonging to independent research into the origin of the tendencies and habitual courses of reflection characteristic of our mental procedure. His first concern is to be true to his fundamental position, 'that all our simple ideas in their first appearance are derived from simple impressions which are correspondent to them, and which they exactly represent.' His next is to trace, with the most painstaking care, the manner in which men come to think as they do of the relations of things external, and of their own doings and destiny. Only a brief outline of his method can be given here.

Impressions and ideas are passing incidents, quickly vanishing from our consciousness. How then are relations established affording coherence to our experience, and giving to it an enlarged significance? 'When any impression has been present with the mind, it again makes its appearance there as an idea'(23). The impressions ' have gone before to prepare the way' for the ideas, and ' the faculty by which we repeat our impressions ' is either memory or imagination. We note ' that quality by which two ideas are connected together in the imagination,' so that the one 'naturally introduces the other' to consciousness; and also 'the arbitrary union of two ideas in the fancy,' in accordance with some particular circumstance by which 'we may think proper to compare them' (32). Here three ' faculties ' are at work, Memory, Imagination, Comparison. Their nature is not specially considered, but rather the 'association of ideas.' 'This uniting principle among ideas 'is ' as a gentle force which commonly prevails,' as appears in the common features of language, ' nature in a manner pointing out to everyone those simple ideas which are most proper to be united into a complex one.' Such references to the action of 'nature' are frequent. The qualities by which ' the mind is after this manner conveyed from one idea to another' are Resemblance, Contiguity in time or place, and Cause and Effect. We enter on the exercise of comparison, discrimination, classification, and inference. We are within the recognised province of Intellect and Will. Hume does not, however, deal with the exercise of these in a prominent way. He does, indeed, occasionally allude to the fact that ' we accompany our ideas with a kind of reflection' (52), and, referring to power and activity, he remarks that ' when a person is possessed of any power, there is no more required to convert it into action, but the exercise of the Will' (30). These are, however, only occasional references. He is much more occupied with 'association of ideas' as 'the gentle force which commonly prevails,' under conditions not generally noted by us. His service to philosophy is most manifest in this direction, while things, as well as ideas, come largely into view.

Cause and Effect may be selected as the most important of the relations named, the treatment of which is most characteristic of our author. Resemblance is readily restricted to ideas, but subsequent references apply to the outer world. 'As the senses, in changing their objects, . . . take them as they lie contiguous to each other, the imagination must by long custom acquire the same method of thinking' (28). But 'there is no relation which produces a stronger connection in the fancy, and makes one idea more readily recall another than the relation of cause and effect betwixt their objects' (28). Cause concerns change and motion, as well as origin of existence, and so bears on our observations first, and on philosophic thought afterwards. A cause is that which under existing conditions produces change in the order of things. We deal no longer with sensory impressions, but with things as related to each other. Hume's statements recognise this. Causality is ' the power by which one object produces another' (126). 'Cause and effect are relations of which we receive information from experience' (r2 6). Experience places us in relation with the external, so that we are constantly influenced by the conditions around us, and that to a degree much greater than particular impressions entail. Hence the need for referring not only to impressions and ideas, but also to objects, to physical laws, and to the action of nature. Allusions to those abound in Hume's Treatise, but without deliberate treatment of the problem as to the relation of impressions to objects. There is, however, necessary reference to adequate and inadequate 'ideas,' and it is assumed that 'wherever ideas are adequate representations of objects, the relations, contradictions, and agreements of the ideas are all applicable to the objects' (58).

The following are examples of Hume's more general statements as to Causation. Causality is 'the power by which one object produces another' (126). 'It is only causation which produces such a connexion as to give us assurance, from the existence or action of one object, that it was followed or preceded by any other existence or action' ^33). 'To begin regularly we must consider the idea of causation, and see from what origin it is derived, . . . examining that primary impression from which it arises' (134). It is granted that 'the idea of Cause' is within consciousness, the problem concerns its entrance.

Our author's first effort is to fence round the area of research. This is done by a series of negatives which will be admitted. (1) 'The power by which one object produces another is never discoverable merely from their idea '(126); nor (2) ' from abstract reasoning or reflection' (126). (3) 'There is no single phenomenon, even the most simple, which can be accounted for from the qualities of the objects as they appear to us'; or (4) ' which we could foresee without the help of our memory and experience' (126) This, then, is Hume's grand difficulty. If ' nothing is ever really present with the mind but its perceptions, or impressions and ideas' (123), and if ' the qualities of the objects as they appear to us' do not include 'the power by which one object produces another,' whence comes the conception of Cause?

For an answer we must turn to the objects and their relations. 'Let us, therefore, cast our eye on any two objects, which we call cause and effect, and turn them on all sides, in order to find that impression which produces an idea of such prodigious consequence' (135). Coming soon to admit that ' there is a necessary connexion,' he says, 'Here again I turn the object on all sides ' (139). The phrase is a favourite one, indicating his reliance on carefully derived observation rather than on casual impressions, such as come to the non-reflective mind, and declaring how difficult is the pass over these mountains. How can we rise from the fleeting impressions, and from their ' double,' to recognise the fixed or the ' necessary' in nature and in thought ? That this elevation is reached, even by ordinary minds independently, is a familiar fact; yet is the exercise one of very striking character, for ' the mind in its reasoning from causes or effects carries its views beyond these objects which it sees or remembers' (r48). Without parting company with its 'impressions and ideas,' it transcends them all, and also those efforts of memory by which those are recalled. The 'necessary' in thought, and also in nature itself, is as superior to ' common experience ' as the mountain height is above the stream in the valley. Even ' to turn the objects on all sides' will help us no more than our lifting of stones from the bed of the stream and turning them in our hands before throwing them back will help us in climbing to the heights above. When we speak of ' invariable sequence,' and 'uniformity of nature,' and of 'necessary connection,' 'we always conclude there is some secret cause' (133), as to which experience carries no witness. Experience leaves all in uncertainty—the issue is doubt—a sceptical philosophy, thinking and speaking of that which is beyond our reach, yet sorely puzzled by a persistent reference to the necessity of a cause, which all affirm, and yet which experience does not warrant. The Philosophy exploring the valley finds no approach to the pass by which to cross into the region beyond. ' Some secret cause' is still our phrase.

At this point curiosity is greatly quickened as Hume's steps are watched. ' The idea of causation must be derived from some relation among objects' (136). 'What, then, are the features of this relation, which is of greater importance than any other?' Objects considered as causes or effects are (1) contiguous; (2) cause is prior to the effect; (3) ' there is a necessary connection to be taken into consideration;' and this third feature is of greater importance' than the other two relations, for contiguity of place and priority in time are not peculiar to the relation under consideration. When we speak of the necessity of a cause, and when the recognition of this necessity stimulates our enquiry and regulates our reasoning, there seems an ultimate principle which impressions and their ideas do not originate.

Pressed by this difficulty, Hume devotes a section of the Treatise to the question, 'Why a cause is always necessary' (I. iii. 3, p. 141). 'It is a general maxim in philosophy that whatever begins to exist must have a cause of existence. This is commonly taken for granted in all reasonings without any proof given or demanded. It is supposed to be founded on intuition, and to be one of those maxims which, though they may be denied with the lips, it is impossible for men in their hearts really to doubt of ' (142) This is very different from fastening the eyes on ' particular effects,' and thereafter searching for their 'particular causes.' When we say that 'a cause is always necessary,' we maintain a general truth which cannot be established by any number of particulars, or even by a whole lifetime of experience. The recognition of the maxim, and the search for a particular cause adequate to account for a particular effect, are exercises of mind quite distinct, the one implying certainty, the other ignorance, which can be dispelled only by observation. Hume's enquiry is concerned with the former of these questions, the warrant for the general maxim 'that whatever begins to exist must have a cause,' and the claim that this maxim is held by men ' without any proof given or demanded.' His method is to ' examine this maxim by the idea of knowledge above explained,' that ' nothing is ever really present with the mind but its perceptions, or impressions and ideas.' But this maxim cannot be included among impressions; we seem in danger of making a theory the test of fact, rather than fact the test of theory. ' All certainty arises from the comparison of ideas, and from the discovery of such relations as are unalterable, so long as the ideas continue the same' (142). These relations are, resemblance, proportions, degrees of quality, and contrariety. None of these 'are implied in this proposition, Whatever has a beginning has also a cause of existence.' What then ? Cause is not an impression, and cannot be its double. The relation of cause and effect is distinct from all the relations enumerated. We cannot, indeed, demonstrate ' the impossibility there is that anything can ever begin to exist without some productive principle.' 'The general maxim in philosophy' is, however, held ' without any proof given or demanded.' The attempted demonstrations of Hobbes, Clarke, and Locke are unavailing. Hence it seems open to Hume to retreat upon his favourite position. ' Since it is not from knowledge or any scientific reasoning that we derive the opinion of the necessity of a cause to every new production, that opinion must necessarily arise from observation and experience' (r47). How, then, is the popular opinion, the 'maxim in philosophy,' the proposition 'whatever has a beginning has also a cause of existence' to be vindicated? His course is a retreat from the principle to particular occurrences, as these stand related to particular causes. 'The next question should naturally be, how experience gives rise to such a principle? But as I find it will be more convenient to sink this question in the following, Why we conclude that such particular causes must necessarily have such particular effects, and why we form an inference from one to another? we shall make that the subject of our future enquiry. It will, perhaps, be found in the end that the same answer will serve for both questions ' (p. 148).

This expectation, sounding oddly from one who professes only a knowledge of particulars in experience, appears at the close of section 3 of the third Part of the Treatise, and not till section 14 do we reach ' the idea of necessary connexion' (p. 272). These 120 pages are occupied with discussions as to the characteristics of our reasonings, dependence on memory, probability, association of ideas, opinion or belief joined to conceptions of things, custom, operating in an oblique and artificial manner, influence of contiguity and resemblance as assisting the conception of cause and effect, formation of general rules, credulity, effects of education, influence of belief, perception of pain and pleasure, the idea of good and evil as actuating the will, effects on the imagination, mixture of truth and falsehood, likelihood and probability, the slow steps by which our judgment arrives at a full assurance, strong tendency to continue in an accepted course, direct and subsidiary or oblique influence of habit, transference of the past to the future; 'all reasonings are nothing but the effects of custom.'

From this extended discussion it will be enough to select the references to causality, which will enable the reader to trace the general line of thought. Even when the mind carries its reasonings from causes or effects beyond objects seen or remembered, 'it must never lose sight of them entirely.' ' We must establish the existence of causes' (r48). 'As to those impressions which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and it will always be impossible to decide with certainty whether they arise immediately from the object, or are produced by th'e creative power of the mind, or are derived from the author of our being' (r52). 'The inference we draw from cause to effect is not derived merely from a survey of particular objects' (155). Even 'contiguity and succession' do not prove sufficient; our reliance is largely on constant conjunction, but this implies no more than this, 'that like objects have always been placed in like relations of contiguity and succession,' a fact which is insufficient to warrant the assertion of ' necessary connexion' (157). Thus 'this new discovered relation of a constant conjuncture seems to advance us but very little in our way.' 'Our memory presents us only with a multitude of instances,' and it must be confessed that ' from the mere repetition of any past impression, even to infinity, there never will arise any new original idea, such as that of a necessary connexion' (158). The investigation is thus in danger of closing in a recognition of ' continuity in nature' as a fact in history, not in an explanation of the philosophic maxim. A sense of helplessness seems to come over the investigator, who is constrained to confess that 'from the mere repetition of any past impression, even to infinity, there never will arise any new original idea, such as that of a necessary connexion' (158). 'Even after the observation of the frequent or constant conjunction of objects we have no reason to draw any inference concerning any object beyond those of experience ' (245). The alleged ' necessity ' has disappeared, vanishing into the gathering of unsolved problems, whose accumulation contributes to the building up of a sceptical philosophy. Yet this search for particular causes would never have been instituted but for the belief ' commonly taken for granted in all reasonings, without any proof given or demanded,' that 'whatever begins to exist must have a cause of existence' (141). While trusting Experience to its utmost extent, we may possibly be constrained to admit that it does not account for all our thoughts. However far our observations and reasonings are pushed, we cannot complete our demonstration. The small success ' has at last obliged philosophers to conclude that the ultimate force and efficacy of nature is perfectly unknown to us, and that it is in vain we search for it in all the known qualities of matter ' (279). 'Suppose two objects to be presented to us, of which the one is the cause and the other the effect, it is plain that from the simple consideration of one or both these objects we shall never perceive the tie by which they are united' (285). All that can be said is this, that after 'a sufficient number of instances we immediately feel a determination of the mind to pass from one object to its usual.attendant.' This determination is unexplained; custom prevails. 'The several instances of resembling conjunctions lead us into the notions of power and necessity. . . . These instances have no union but in the mind which observes them and collects their ideas. . . . Necessity then is the effect of this observation, and is nothing but an internal impression of the mind, or a determination to carry our thoughts from one object to another ' (289). This is only necessary determination of our thoughts, leaving unexplained our fundamental maxim, ' the necessity of a cause for every occurrence.' How he regards this result appears from these words—' I am sensible that of all the paradoxes which I have had, or shall hereafter have occasion to advance in the course of this treatise, the present one is the most violent' (291).

The main features of Hume's intellectual philosophy are now before the reader. Our limits prevent our dealing with his analysis of the passions and his theory of the basis of moral distinctions. My leading purpose has been to make clear what is to be understood by Hume's scepticism. It is distrust of everything which transcends our sensory impressions and the ' copies' of them. All certainty is reduced to passing impression and its passing influence. There is no direct evidence as to the nature of matter or of mind. He esteems these his chief ' discoveries' in philosophy, the exact correspondence of impressions and ideas; that association of ideas under custom is the utmost reach of the understanding; that the knowledge of a cause is unattainable, and that ' the very essence of belief consists in the force and vivacity of the conception.'

The first volume of the Treatise does not conclude without acknowledgment of the sense of his own perplexity and misgiving, which has an autobiographic value of the highest degree. ' The intense view of the manifold contradictions and imperfections in human reason has so wrought upon me and heated my brain, that I am ready to reject all belief and reasoning, and can look upon no opinion even as more probable or likely than another. Where am I, or what? From what causes do I derive my existence, and to what condition shall I return? Whose favour shall I court, and whose anger must I dread? What beings surround me, and on whom have I any influence, or who have any influence on me? I am confounded with all these questions, and begin to fancy myself in the most deplorable condition imaginable, environed with the deepest darkness, and utterly deprived of the use of every member and faculty.

'Most fortunately it happens that, since reason is incapable of dispelling these clouds, nature herself suffices to that purpose and cures me of this philosophic melancholy and delirium, either by relaxing this bent of mind, or by some avocation and lively impression of my senses, which obliterate all these chimeras. I dine, I play a game of back-gammon; I converse, and am merry with my friends; and when after three or four hours' amusement, I would return to these speculations, they appear so cold, and strained, and ridiculous, that I cannot find in my heart to enter into them any farther.'

Still, ' I cannot forbear having a curiosity to be acquainted with the principles of moral good and evil, the nature and foundation of government, and the cause of those several passions and inclinations which actuate and govern me. I am uneasy to think I approve of one object and disapprove of another ; call one thing beautiful

and another deformed; decide concerning truth and falsehood, reason and folly, without knowing on what principles I proceed'(466-470).

The reception given to the Treatise was disappointing to Hume. It did not on its appearance awaken any marked interest. But its effect on human thought was deep and lasting. A new epoch in philosophy follows directly from it. Scepticism results in a stronger faith. The effect on philosophy was quickening. Theology was differently affected. It was resentful and actively antagonistic. The assault was delivered from a remote point; but, on that account, it seemed all the more unsettling; in challenging the foundations of all certainty, it threatened religious faith by involving all belief in common disaster. To the theologians of the day, who were the most earnest and devoted expounders of Christianity, Hume was the arch-sceptic—the adversary of religion. Their attitude towards him was, however, determined more by their profound sense of the interests involved, and of the consequences to the country which would follow a period of unsettled faith, than by an exact and far-reaching survey of his philosophic positions.

In the region of philosophy, the result was altogether a gain. Hume led the way into the enquiry as to the Origin of our impressions and convictions and habits of thought. He opened up the large question concerning the synthesis of knowledge. He tested empirical philosophy by asking whether all things are not involved in uncertainty, if experience is only a succession of sensations, vanishing in less vivid copies. His research involved constant reference to objects and their relations and continual allusion to the action of mind, involving imagination, thought, will, custom, and general principles. Hume's references to the mind or soul possess special interest and are of frequent occurrence. Of these, there are three which deserve to be quoted. They occur when his investigations into ' the extent and force of the human understanding ' is far advanced. 'What we call a mind is nothing but^aj3£ap,sr c.Qlle^orypfjlifferent perceptions, united together by certain relations, and supposed, though falsely, to be endowed with a perfect simplicity and identity' (361). 'The mind is a kind of theatre where several perceptions successively make their appearance; pass," repass, glide away, and mingle in an infinite variety of postures and situations. . . . The comparison of the theatre must not mislead us. They are the successive perceptions only that constitute the mind; nor have we the most distant notion of the place where these scenes are represented or of the materials of which it is composed' (439). 'I cannot ,compare the. soul more properly to anything tlia'n to a republic or: commonwealth, in which the several members are united by the reciprocal ties of government and subordination, and give use to other persons who propagate the same republic in the incessant changes of its parts. And as the same individual republic may not only change its members, but also its law and constitutions, in like manner the same person may vary his character and disposition, as well as his impressions and ideas, without losing his identity' (453). The sceptical bias is marked, but there is a sense of the inevitable acknowledgment of an individuality — an identity of * These passages occur thus—I., iv. sec. 2 ; sec. 6; sec. 6.

being and a power of direction of conduct. The breadth of significance involved may be seen, when Hume says in preparing the way for the quotation last given—' The true idea of the human mind is to consider it as a system of different perceptions or different existences which are linked together by the relation of cause and effect, and mutually produce, destroy, influence, and modify each other' (453). The passages do not readily coalesce in a consistent and coherent representation of the understanding, but they come as near to each other as seems possible in a sceptical philosophy, declaring ' that all the nice and subtle questions concerning personal identity can never possibly be decided.' The author does not escape the confession of his own despair,—' For my part, I know not what ought to be done in the present case.' ' A true sceptic will be diffident of his philosophical doubts, as well as of his philosophical conviction.'

Hume's references to Nature (27, 211, 321, 374,) will specially interest the student of mental philosophy. His service to philosophy was great even with 'his miscellaneous way of reasoning' (i., 457) His scepticism gave a fillip to deeper thought; it awakened new interest in the thinking view of things ; it roused to fresh effort the men who were in danger of being satisfied with dogmatic formulae. It brought a searchlight on Empiricism, exposing its weakness; it disclosed the large demands which philosophy makes on Reason; it lifted the question as to ' the extent and force of the human understanding' into a position of first rank; it introduced a new epoch, full of fenergy, enthusiasm, and expectation. These results came slowly; we cannot wonder that the author was disconcerted and disheartened by lack of evidence of their approach; but they came surely; yet not in such form as was expected by the pioneer, who whetted his axe so eagerly and dealt his blows with an energy which had gathered force from daily exercise.

Hume's native land was roused. The 'Scottish Philosophy' was the fruit of his scepticism—the philosophy of 'common sense,' resting on ' principles' or essential conditions of the understanding, without reference to which no explanation of Experience is possible. The answer came first, in critical form, from another Hume—Henry Home, Lord Kames; more slowly and systematically from Reid, Stewart, and Hamilton, Scotland's leaders in the march for 'a thinking view of things.' A deeper and more elaborate answer came from Kant, who confessed that he had been roused by Hume from dogmatic slumber. Kant's contribution consisted of a critical examination of the conditions of human knowledge—a marvel of acumen, which has taxed the acuteness of later thinkers for its exposition and criticism, and has given to the synthesis of human knowledge a new meaning. To Hume's scepticism we owe the transcendental philosophy of Germany, through all the developments of Kantian and Hegelian thought onwards to ' the return upon Kant' more recently proclaimed. The reception of the Treatise was such that he afterwards seemed ' anxious to disconnect himself with the authorship' (Burton, I., r36), or, otherwise, to describe it as a 'juvenile work,' 'projected before he left college' (Advertisement to Essays). On the other hand, he claims that ' most of the principles and reasonings contained in this volume' of Essays were ' published' in the Treatise;

and then he adds, 'not finding it successful, he was sensible of his error in going to the press too early; he cast the whole anew in the following pieces.' Whatever may have been the advantages in respect of the more popular form of the Essays, most students of the earlier and later works will concur in the judgment of Huxley as to their merits, when he says, concerning the Inquiry,—' In style, it exhibits a great improvement on the Treatise; but the substance, if not deteriorated, is certainly not improved' (Huxley's Hume, p. 11).