The suggestion illustrates the bent of Reid’s thought in later life. If our common sense of the continuous independent existence of sensible things, and of their manifestation in Perception as directly as states of our own minds are manifested to us when we are conscious of them—if _this_ was the factor of the Common Sense that engaged him in New Machar and King’s College days, the Power or Causality which all changes in the universe presuppose now becomes prominent, alike in his correspondence and in his books. What is meant by Power, and where is the Power centred that is implied in the changes that are always going on, in ourselves and in our surroundings? Priestley’s assumption that matter explains all the phenomena of a human mind; the theory of universal necessity advocated by Kames; and the duties of his Glasgow professorship, all tended to carry his reflections onward from the merely physical to the ethical judgments of the common sense, and so upward from the merely natural to the spiritual interpretation of the universe. ‘First that which is natural, then that which is spiritual.’ This runs through his correspondence with Lord Kames. That there is no absolute necessity for men being bad; that their immoral acts are centred and originate in themselves and not in God; that it would be unjust to exact as a duty what it is not in a person’s power to do; that what a man does voluntarily or with deliberate intention, it is also in his power not to do; that what is done without his will is not really done by _him_ at all; and that real power is moral agency,—these are ultimate judgments, reached ‘not by logical reasoning,’ but in ‘the more trustworthy way of immediate perception and feeling,’ to which Reid so often appeals. ‘If I could suppose God to make a devil a devil, I cannot suppose that He would condemn him for being a devil,’ is in a letter to Lord Kames.[21] The impotence of matter rather than its independence is now insisted on; with the inference that at any rate _it_ cannot cause our perceptions, as Priestley supposed. He begins to see that power must be referred to mind or spirit alone, and that matter is powerless. ‘Efficient causes are not within the sphere of natural philosophy, which is concerned only with the laws or methods according to which Power operates. It exhibits the grand machine of the material world, analysed, as it were, and taken to pieces. It belongs to metaphysics and natural theology to show the Power that continues and gives motion to the whole; according to laws which the naturalist discovers, and perhaps according to laws still more general.’ * * * * *