these philosophers,’ Dr. Priestley said, ‘it will appear that they are saying one thing and doing another—talking plausibly about the necessity for admitting axioms as the foundation of all reasoning, but meaning to recommend particular assumptions of their own as axioms—not as being founded on perception of the agreement of ideas, which is the great doctrine of Mr. Locke, and which makes truth to depend upon the necessary nature of things, to be therefore absolute, unchangeable, and everlasting, but merely on some unaccountable instinctive persuasions, depending upon the arbitrary constitution of our nature—which makes all truth be relative to ourselves only, and consequently to be infinitely vague and precarious. This system admits of no final appeal to reason properly considered, which any person might be at liberty to examine and discuss; on the contrary every man is taught to think himself authorised to pronounce dogmatically upon every question, according to his present feeling and persuasion, under the notion of its being something original, instructive, and incontrovertible; although, stoutly analysed, it may appear to be mere prejudice.’ Thus, as opposed to the man of straw he set up under the name of Reid, Priestley postulated a materialistic conception of man, as only an organism, the so-called mental and moral power of which was the natural issue of physical structure; his perceptions the effects of their own objects; and on the whole a necessitated system of the universe, which excluded morally responsible agency. Reid made no reply at the time to this argumentative discharge. In an unpublished letter to Dr. Price he gives a reason for his silence. ‘I will not answer Dr. Priestley,’ he says, ‘because he is very lame in abstract reasoning. I have got no light from him. And indeed what light with respect to the powers of the mind can one expect from a man who has not yet learned to distinguish ideas from vibrations, nor motion from sensation, nor simple apprehension from judgment, nor simple ideas from complex ideas, nor necessary truths from contingent truths?’[20] In 1775 Reid writes to Lord Kames:—