true that this general proposition is derived from the particular and
earlier one. I must first realize in my own experience that, as thinking, I
exist, before I can reach the general conclusion that thought and existence
are inseparable. This fundamental truth is thus not a syllogism, but a
not further deducible, self-evident, immediate cognition, a pure
intuition--_sum cogitans_. Now, if my existence is revealed by my activity
of thought, if my thought is my being, and the converse, if in me thought
and existence are identical, then I am a being whose essence consists in
thinking. I am a spirit, an ego, a rational soul. My existence follows only
from my thinking, not from any chance action. _Ambulo ergo sum_ would not
be valid, but _mihi videor_ or _puto me ambulare, ergo sum_. If I believe
I am walking, I may undoubtedly be deceived concerning the outward action
(as, for instance, in dreams), but never concerning my inward belief.
_Cogitatio_ includes all the conscious activities of the mind, volition,
emotion, and sensation, as well as representation and cognition; they are
all _modi cogitandi_. The existence of the mind is therefore the most
certain of all things. We know the soul better than the body. It is for
the present the only certainty, and every other is dependent on this, the
highest of all.

What, then, is the peculiarity of this first and most certain knowledge
which renders it self-evident and independent of all proof, which makes
us absolutely unable to doubt it? Its entire clearness and distinctness.
Accordingly, I may conclude that everything which I perceive as clearly and
distinctly as the _cogito ergo sum_ is also true, and I reach this general
rule, _omne est verum, quod clare et distincte percipio_. So far, then, we
have gained three things: a challenge; to be inscribed over the portals
of certified knowledge, _de omnibus dubitandum_; a basal truth, _sum
cogitans_; a criterion of truth, _clara et distinct a perceptio_.