Reid is explicit that questions about the existence of ether were open questions that were not settled by a priori (EIP 2.3, 82).
Reid exemplifies his commitment to the unaccountability of memory experience by placing a first principle about memory in his set of first principles of contingent truths: "That those things did really happen which I distinctly remember" (EIP 6.5, 474).
Here Reid echoes Descartes' operational definition of the self in Meditation 2. Reid also argues that persons are not identical to their bodies (EIP 3.4, 264).
Reid corrects this misunderstanding by emphasizing the fact that his first principles are psychological generalizations about belief formation applicable to most of our species (EIP 6.4, 464 5).
Besides, human reason itself is fallible (EIP 2.22, 244 5).
Most of Reid's first principles of contingent truth take the form of Principle 5, which reads "That those things do really exist which we distinctly perceive by our senses, and are what we perceive them to be" (EIP 6.5, 476).
Third, Reid follows Bishop Butler in arguing that Locke's justification of his theory of personal identity is circular (EIP 3.6, 277).
In his work in epistemology and philosophy of mind, which is found primarily in An Inquiry into the Human Mind (IHM) and Essays on the Intellectual Powers of Man (EIP), Reid frames his project as a response to a general position that he calls the Way of Ideas.
The principal philosophical error that led to the reification of universal properties as independent existents is the conflation of the objects of conception with the objects of perception (EIP 4.1, 302 3).
General terms are general due to their referents, but they are particular token conceptions of individuals (EIP 5.2, 360).
The first principle of necessary truth licensing inferences from signs of intelligence to intelligence pairs with another that states that the belief in other minds is also a first principle (EIP 6.5, 484).
