_Summary of Criteria._--The following may be regarded as a summary of the more important criteria by which to distinguish primary truths from all others.
_a._ As first truths, or primary data of intelligence, they are, of course, not derived from observation or experience, but are prior and necessary to such experience.
_b._ They are _simple_ truths, not resolvable into some prior and comprehending truth from which they may be deduced.
_c._ As simple truths, they _do not admit of proof_, there being nothing more certain which can be brought in evidence of them.
_d._ While they do not admit of proof, _the denial of them involves us in absurdity_.
_e._ Accordingly, as simple, and as self-evident, they are universally admitted.
_Enumeration of some of the Truths usually regarded as primary._--Different writers have included some more, some fewer, of these first principles in their list; while no one has professed, so far as I am aware, to give a complete enumeration of them. Such an enumeration, if it were possible, would be of great service in philosophy. The following have been generally included among primary truths by those who have attempted any specification, viz.; our personal existence, our personal identity, the existence of efficient causes, the existence of the material world, the uniformity of nature; to which would be added, by others, the reliability of memory, and of our natural faculties generally, and personal freedom or power over our own actions and volitions.
_Correctness of this Enumeration._--That the truths now specified are in some sense primary, that they are generally admitted and acted upon, among men, without process of reasoning, and that, when stated, they command the universal and instant assent of even the untaught and unreflecting mind, there can be little doubt. Whether, in all cases, however, they come strictly under the rules and criteria now given; whether, for example, our own existence and identity are primary data of consciousness; or whether, on the contrary, they are not _inferred_ from the existence of those thoughts and feelings of which we are directly conscious, as, for example, in the famous argument of Descartes, _Cogito, ergo sum_, may admit of question.