Psychologia Empirica

§. 12.

The certainty of that foundation.

That we are conscious of ourselves is confirmed by the very act of doubting. For suppose you doubt whether you are conscious of yourself and of other things outside of yourself, or not. You cannot deny that you are doubting, since you affirm this yourself (§. 28 Ontol. & §. 205 Log.). But whence do you know that you are doubting, if not from the fact that you are conscious of your own doubting? By this very act, therefore, you affirm that you are conscious of yourself when you assert that you are doubting regarding it. That you are, therefore, conscious of yourself is confirmed by the very act of doubting.

We shall use this principle to demonstrate the degree of evidence upon which the cognition of the existence of oneself, or, if you prefer, of the soul, rests.

§. 13.

The principle of knowing the existence of oneself.

Whoever is actually conscious of himself and of other things, he also actually is or exists. This proposition is so evident that it must be granted without proof, and thus it should be taken as an axiom. But if you deny this, it must be posited that some being could be actually conscious of itself and of other things, even if it does not itself actually exist. Therefore, certain things would inhere in it actually before it exists: which, since everyone would confess to be absurd, it follows that whoever is conscious of himself and of other things exists.

The present proposition is a special case of the common notion by force of which we infer the existence of a thing. For from actual predicates, the existence of a thing is commonly inferred. If someone says that a stone is hot, that the sun is shining, or that a seed is germinating, he is speaking of a singular case: no one will doubt that one may infer from this that the stone, the sun, or the seed exists. Thus, there is given in us a certain common notion, to which, when distinctly enunciated, this proposition corresponds: If anything actually belongs to an individual, or, if you prefer, if anything can actually be predicated of an individual, the same actually is, or exists. That the present proposition is a special case of this general notion is evident in itself. And indeed, by this very principle, the cognition of the existence of our soul is reduced to a common notion. It is useful here to compare what we have said elsewhere to this end (not. §. 370 & 393, and likewise not. §. 203 & 186 Ontol.) and what we have warned concerning the utility of this reduction (not. §. 125 Ontol.). Would that philosophers paid more attention to common notions.