 In addition to assuring ourselves of the indubitability of the knowledge of our own existence (cf. Euler 2003), this initial consideration supplies a touchstone for what will count as demonstratively certain, but also provides the elements for a nominal definition of the soul. Thus, the soul is identified just as “that being in us which is conscious of itself and other things outside of it” (EP: §20) which, as an existing thing, can serve as the object of empirical psychology.