I say, then, that we have the knowledge of OUR OWN existence by intuition; of the existence of GOD by demonstration; and of OTHER THINGS by sensation.
3.

Our Knowledge of our own Existence is Intuitive.
As for OUR OWN EXISTENCE, we perceive it so plainly and so certainly, that it neither needs nor is capable of any proof for nothing can be more evident to us than our own existence.

I think, I reason, I feel pleasure and pain: can any of these be more evident to me than my own existence?
If I doubt of all other things, that very doubt makes me perceive my own existence, and will not suffer me to doubt of that.

For if I know I feel pain, it is evident I have as certain perception of my own existence, as of the existence of the pain I feel: or if I know I doubt, I have as certain perception of the existence of the thing doubting, as of that thought which I CALL DOUBT.

Experience then convinces us, that we have an INTUITIVE KNOWLEDGE of our own existence, and an internal infallible perception that we are.