Between theology and philosophy in the earlier stages there is a natural affinity. Theology, in the orthodox sense, busies itself with the systematizing of the doctrines of revelation, while philosophy busies itself with their intellectual comprehension. The relation between the two is clearly shown in the saying of Anselm: "I believe in order that I may understand." As the fundamental demand made by the Church of the Middle Ages upon the human mind was belief, it is easy to see that philosophy was used not in the independent pursuit of truth, but in order to make reason harmonize with faith. For this purpose great use was made of Aristotle's philosophy so far as it was understood. Here was laid the foundation of the huge system known as Scholasticism, which kept the human mind in bondage till the Reformation, or rather the Renaissance. In truth the Reformers were in no mood to study the philosophical side of the conflict with Rome; indeed in the reformed universities Aristotle was dominant till towards the close of the sixteenth century. Ultimately Aristotle was dethroned, but it was not till the Revolution that Scotland got breathing space for the consideration of the problems of philosophy in the modern sense of the term.

Philosophy, like theology, deals with the great subjects, God, the universe, and man; and by carefully noting the attitude of the various thinkers to these three questions we shall be able to trace the evolution of Scottish philosophy. When Francis Hutcheson, the father of Scottish Philosophy, began to busy himself with metaphysical inquiries a new method had come into vogue, the inductive with its respect for facts in place of the scholastic with its endless word-spinning and dialectical gymnastics. Locke set the fashion by refusing to soar into transcendental regions, and by insisting upon an examination of the powers of the human mind, so as to gauge its capacity for dealing with the great problems of existence. The method of Locke was followed by Hutcheson, though not slavishly. In the sphere of Ontology he rejected the Cartesian demonstration of the existence of God, and, true to the inductive principle, based the defence of Deism on the argument from Design. He finds Locke's system helpful in his conflict with Calvinism, and the doctrine of natural depravity he opposes by the utilitarian theory of morals with its all-embracing optimism.

As it was the avowed object of the Moderates, in the phrase of Hutcheson, to put a new face on theology, they found the philosophy of Locke admirably suited for their purpose. Hutcheson had no desire to deny the supernatural, he ignored it. He set himself to construct a scheme of thought which, without doing violence to Scottish beliefs, would substitute a thinly veiled rationalism for the Calvinism of the Kirk. While rejecting the Cartesian demonstration of the existence of God, he found it necessary to use the Deity as a kind of philosophic figure-head. The idea of God which Descartes based on innate ideas Hutcheson, following Locke, traced to an empirical origin; but in the deistical creed of the Scottish Moderates God reigned but did not govern. Experience, not revelation, was to be made the starting-point of the thought of the future. This is clearly seen in the ethical side of Hutcheson's philosophy. He seeks the sanctions of morality not in revelation, but in the constitution of human nature. By the aid of Locke, Hutcheson thought it possible to retain enough of the theological dogmas to constitute a kind of natural religion, while at the same time making experience and the study of human nature take the place of the fervid supernaturalism of the Confession of Faith.

But a change was to come over the philosophic optimism of the deistical school. David Hume appeared upon the scene, and delivered a series of deadly blows at the Lockian philosophy. Locke not only asserted that all knowledge was built out of experience; he set himself to describe the process. He found ideas to originate in sensation and reflection. External objects mirrored themselves in the mind, and by means of reflection were converted into ideas. So much for the nature and origin of knowledge. What of its validity? If impressions coming through the senses have to be worked up into ideas by reflection before they gain the dignity of knowledge, we have to ask, What is the relation between the objective reality and the subjective ideas? Locke's reply is disconcerting. We must not, he says, think that our ideas are exactly the images and qualities of something inherent in the object. How, then, are we to discover the precise nature of the objective world which we think of as material? Locke recognizes that all the qualities of Matter do not exist as they seem, but are conditioned by the mind. Light and heat, for example, have no objective existence; they exist only in relation to mind. But if the mind clothes Matter with a number of qualities, why not with all? Berkeley saw the dilemma, and endeavoured to extricate Locke from the philosophic quagmire by abolishing Matter as a substance. Spirit, not Matter, said Berkeley, is the real substance of the Universe.

We are now in a position to appreciate fully the intervention of Hume. Berkeley's contention was that there was no evidence of a permanent substance called Matter. To this Hume replied that there was just as little evidence of a permanent substance called Mind. What we are conscious of, says Hume, is not an entity called mind, but a chain of feelings linked together by association. The effect of all this on the theological side of the Lockian philosophy was unsettling in the highest degree. Locke, followed by Hutcheson, made Causation as expressed in the argument of Design a stepping-stone to belief in God. By substituting Association for Causation Hume knocked the foundation from Theology. By resolving mind into a series of feelings, he rendered chaotic the science of psychology. The three great departments of philosophy—ontology, cosmology and psychology, by Hume were driven into bankruptcy.

Hume proved to be an epoch-making force in the history of philosophy. He wakened Kant from his slumbers, and started German thought on its high philosophic career which found its culmination in the all-embracing system of Hegel. Meanwhile, what we have to deal with is not the German, but the Scottish, answer to Hume. His most resolute opponent was Reid. Reid has never been estimated at his real value. Looked upon as the philosopher of common sense, the representative, so to speak, of the average man, Reid has been treated as a kind of intruder in the philosophic arena. No one would think of placing him alongside the German opponents of Hume, but it is a striking fact that between the answers of Reid and Kant there is a remarkable resemblance. Reid saw the great issues which were at stake. If Hume's views were to prevail, religion and all that pertained to the higher side of life would fall under eclipse. If these views were to be overturned Reid recognized that Hume's errors must be attacked at the root, namely, the Lockian theory of mind. Accordingly Reid joined issue with Locke. As I have dealt with this part of the subject in my volume Books to Bead and How to Bead Them, I may be permitted to reproduce the following sentences:—

"Reid declared that the mind was not a blank organism, the passive recipient of the impressions of the senses. According to Reid, the mind is originally endowed with a definite structure and equipment with which it o-ceeds to interpret experience. In his view every perception implies a judgment. We do not, as Locke has it, first collect our isolated impressions, and then classify and compare them; in the very act of perception we are exercising judgment. Now whence comes this capacity of judging ? Clearly not from experience, as without judgment there could be no experience for us. Reid's great claim to the regard of philosophers is that he was the first who detected the only effective weapon with which to meet Hume. Strictly speaking, Kant simply founded his whole system on the fruitful suggestion of Reid—namely, that before experience itself is possible, before the impressions of sense can even make themselves known, there must exist a self-conscious mind whose structure is not created by experience, but which needs experience to set it to work."

It is a tribute to Reid's power that his influence extended beyond his native land; along with Hume he took from Scottish philosophy the reproach of parochialism. In their contest with the materialistic theories of their time the French thinkers like Jouffrov and Cousin found in Reid a formidable ally. In the words of Cousin: "It would be impossible to write a history of Scotland in the last half of the eighteenth century without meeting everywhere in the numerous and remarkable productions of the Scotch genius of this epoch the noble spirit which that genius excited, and which in its turn has communicated to it a new force."

Scotland in the eighteenth century produced quite a crop of thinkers of a philosophic turn of mind, among whom may be mentioned Campbell, Oswald, Beattie, Lord Monboddo, Adam Smith, etc., but inasmuch as they struck no orginal vein of thought, opened no new avenues of metaphysical inquiry, they need not detain us long. Upon the shoulders of Dugald Stewart fell the mantle of Reid. Stewart was more a rhetorician than a philosopher; his work might be summed up in the remark that he gave literary form to the system of his master, and kindled in the breasts of a generation of students a noble enthusiasm for the higher things of the mind. Nor does Thomas Brown, Stewart's successor, call for detailed mention. His name is associated with one department of psychology rather than with fundamental problems, a department which occupied also the attention of Hume—the relation of Cause and Effect, in which he departed considerably from the traditional treatment of the Scottish school.

But the day of small men was passing away. A giant appeared in the person of Sir William Hamilton. In his hands Scottish philosophy not only revived, but acquired a world-wide reputation. Hume's speculations had brought forth showers of pamphlets, but they never had been laid to rest. In philosophical circles an uneasy feeling prevailed that the last had not been heard of this troubler in Israel. Reid had spent his force upon Hume, but the task of demolition had been left unfinished. To the task Hamilton, in the spirit of Reid, addressed himself. Hume by his summary treatment of Mind and Matter had left nothing stable in the universal flow; personal identity itself seemed something quite elusive. Hamilton took his stand on Consciousness. Consciousness of personal identity and of an objective material world—upon those two necessary beliefs, which are presupposed in all intellectual activity, hang all our knowledge. Again we come back to the question which troubled Reid. What is the nature of this objective existence which we call the world ? Hamilton called himself a natural Realist after the manner of Reid, whose theory he stripped of its crudeness, though there are those who think that Reid would have difficulty at times in recognizing his own views in the revised version. If Hamilton's speculations did not satisfy the conditions of an absolutely sound theory, they had one great merit—they gave a great impetus to psychological thought, and by rousing into activity the powers of John Stuart Mill, and raising fundamental questions, Hamilton linked the Scottish school with the latest aspects of the evolution philosophy.

The problem with which Hamilton's name will always be conspicuously associated is that known as the Relativity of Knowledge. In his famous Edinburgh Review article, Hamilton at one bound sprang into the first rank of thinkers. The remarkable thing is that Hamilton, a professed follower of Reid, whose whole life was spent in combating the philosophic Nihilism of Hume, should practically undo the work of his master. Hamilton did not mean his theory to be pressed into the service of Agnosticism. While admitting the incapacity of thought to deal with the Absolute, he hoped to serve the cause of Theism by falling back upon faith. This part of his philosophy he never welded into organic unity, with the result that the portions which he owes to Reid, and those which he derived from Kant, are left unreconciled. In the words of Professor Laurie in his excellent book on Scottish Philosophy: "If all our knowledge be of the relative and conditioned, and if every attempt to transgress these limits lead us to the realms of non-conceivability or contradiction, then philosophy is not in a position to affirm or to deny anything which may be supposed to stretch beyond. . . . From this point of view Hamilton's philosophy has strengthened the phenomenalism which, issuing from the scepticism of Hume, has assumed a positive form in such writers as Bain and Mill, and has been further encouraged by the progress of modern science in its exclusive search for facts and uniformities. . . . The philosophy of Common Sense, devised by Reid as a safeguard against Scepticism and Idealism, was so transmuted by Hamilton as to lead back again to the conclusion that nothing can be affirmed or denied beyond the fleeting phenomena of consciousness."