P23: The human Mind cannot be absolutely destroyed with the Body, but something of it remains which is eternal.

Dem.: In God/Nature there is necessarily a concept, or idea, which expresses the essence of the human Body (by P22), an idea, therefore, which is necessarily something that pertains to the essence of the human Mind (by IIP13). But we do not attribute to the human Mind any duration that can be defined by time, except insofar as it expresses the actual existence of the Body, which is explained by duration, and can be defined by time, i.e. (by IIP8 C), we do not attribute duration to it except while the Body endures. However, since what is conceived, with a certain eternal necessity, through God/Nature’s essence itself (by P22) is nevertheless something, this something that pertains to the essence of the Mind will necessarily be eternal, q.e.d.

Schol.: There is, as we have said, this idea, which expresses the essence of the body under a species of eternity, a certain mode of thinking, which pertains to the essence of the Mind, and which is necessarily eternal. And though it is impossible that we should recollect that we existed before the Body—since there cannot be any traces of this in the body, and eternity can neither be defined by time nor have any relation to time—still, we feel and know by experience that we are eternal.14 For the Mind feels those things that it conceives in understanding no less than those it has in the memory. For the eyes of the mind, by which it sees and observes things, are the demonstrations themselves.

Therefore, though we do not recollect that we existed before the body, we nevertheless feel that our mind, insofar as it involves the essence of the body under a species of eternity, is eternal, and that this existence it has cannot be defined by time or explained through duration. Our mind, therefore, can be said to endure, and its existence can be defined by a certain time, only insofar as it involves the actual existence of the body, and to that extent only does it have the power of determining the existence of things by time, and of conceiving them under duration.