How Do We Know That

I Did Not Imitate The Skeptics Who Doubt Only For Doubting's Sake, And Pretend To Be Always Undecided; On The Contrary, My Whole Intention Was To Arrive At A Certainty, And To Dig Away The Drift And The Sand Until I Reached The Rock Or The Clay Beneath.

I Am Thing That Thinks: That Is, A Things That Doubts,affirms, Denies, Understands A Few Things, Is Ignorant Of Many Things, Is Willing, Is Unwilling, And Also Which Imagines And Has Sensory Perceptions.

But I Cannot Forget That, At Other Times I Have Been Deceived In Sleep By Similar Illusions; And, Attentively Considering Those Cases, I Perceive So Clearly That There Exist No Certain Marks By Which The State Of Waking Can Ever Be Distinguished From Sleep, That I Feel Greatly Astonished; And In Amazement I Almost Persuade Myself That I Am Now Dreaming.

There Is A Great Difference Between Mind And Body Insomuch As Body Is By Nature Always Divisible, And The Mind Is Entirely Indivisible.

Whatever I Have Up Till Now Accepted As Most True And Assured I Have Gotten Either From The Senses Or Through The Senses. But From Time To Time I Have Found That The Senses Deceive, And It Is Prudent Never To Trust Completely Those Who Have Deceived Us Even Once.