There are passages of Sir W. Hamilton's writings in which he appears to feel that the _introspective_ method alone is insufficient for the interpretation of Consciousness, and that the analytical method must be employed to reinforce it. But on this as on other points he is not always consistent with himself. For in laying down the principle upon which the primary truths of Consciousness, the original data of intelligence, are to be ascertained and distinguished from generalizations out of experience and custom, he declares that the one single and certain mark is Necessity--they must be beliefs which we are under the necessity of believing--of which we cannot get rid by any mental effort. He decides this, of course, for himself, by the _introspective_ method alone. He (with M. Cousin and other philosophers who take the same view) does not apply the analytical method to inquire whether his necessity of belief may not be a purely acquired necessity and nowise congenital. It is, indeed, remarkable that these philosophers do not even seek to apply the introspective method as far as that method will really go. They are satisfied with introspection of their own present minds; without collecting results of the like process as applied to other minds, in different times and places. They declare various beliefs to be necessary to the human mind universally, merely because such is the actual fact with their own minds and with those immediately around them; sometimes even in defiance of proof that there are (or have been) persons not sharing such beliefs, and occasionally even believing the contrary; therefore, when even the introspective method really disallows their affirmative instead of sustaining it. This is, in truth, an abuse of the introspective method; yet even if that method were employed in its fullest extent--if the same incapability of believing otherwise could be shown as common to all mankind--it might still be only the effect of a strong association. The analytical method must still be called in to ascertain whether we are forced to suppose such incapability to be an original fact of consciousness, or whether it may not have been generated in the mind by circumstances under the natural working of the laws of association. It is certain that these laws not only may, but must, give birth to artificial inconceivabilities in the mind--and that some of these may be equal in strength to such, if any, as are natural. 'The History of Science' (says Mr Mill, following out the same train of reasoning which we read in the third Book of his 'System of Logic') 'teems with inconceivabilities which have been conquered; and with supposed necessary truths, which have first ceased to be thought necessary, then to be thought true, and have finally come to be deemed impossible.'--p. 150.