so that the beginning of the one impression is inseparably associated with the departure or cessation of the other. Thus our inability to form a conception always arises from our being compelled to form another contradictory to it."
Our inability to conceive a round square due to the fact "that in our uniform experience, at the instant when a thing begins to be round, it ceases to be square," and to the inseparable association between incipient roundness and departing squareness! Whether any one has ever had such experience as is here described, I do not know; but, if he has, I am confident that, even after being reënforced by a large inheritance of ancestral experience in the light of the modern theory of evolution, it will prove insufficient to account for the inseparable association which Mill brings into play. The simple truth is, that a round square is an absurdity, a contradiction in terms. A square is a figure bounded by four equal straight lines intersecting at right angles; a round figure is a figure bounded by a curve; and the oldest definition of a curve is that of "a line which is neither a straight line, nor made up of straight lines."
It ought to be said that there are expressions in the same chapter of Mill's book, from which I have just quoted, which show that the author was very ill at ease in the presence of his own theory. For instance, he says (ib., p. 88): "These things are literally inconceivable to us, our minds and our experience being what they are. Whether they would be inconceivable if our minds were the same, but our experience different, is open to discussion. A distinction may be made which, I think, will be found pertinent to the question. That the same thing should at once be and not be—that identically the same statement should be both true and false—is not only inconceivable to us, but we cannot conceive that it could be made conceivable."
That so clear and vigorous a thinker as Mill should have been capable (especially when he was grappling with the thoughts of a man like Sir W. Hamilton) of writing these sentences, is indeed wonderful. First, he denies that inconceivability is, in any sense or in any case, a test of truth or reality; but then he says it may be otherwise, if the inconceivability itself is inconceivable! That is to say: a witness is utterly untrustworthy; but, when he makes a declaration respecting his own trustworthiness, he ought to be believed!
That the whole theory of inseparable association, as here advanced and applied by Mill, is without foundation, it being impossible, under his theory, to know what the experience of his numerous readers has been, except again by experience which he cannot have had, since most of these readers were utterly unknown to him—that all attempts to argue questions with any one on such a basis are supremely foolish, Mill being bound, by his own doctrine, to accept the answer, "My experience has been otherwise," as conclusive—that this theory is suicidal and subversive of itself, and that every earnest sentence Mill