I Think; Therefore I Am.

He Lives Well Who Is Well Hidden.

The Greatest Minds Are Capable Of The Greatest Vices As Well As Of The Greatest Virtues.

I Know That I Exist; The Question Is, What Is This 'i' That 'i' Know.

These Long Chains Of Perfectly Simple And Easy Reasonings By Means Of Which Geometers Are Accustomed To Carry Out Their Most Difficult Demonstrations Had Led Me To Fancy That Everything That Can Fall Under Human Knowledge Forms A Similar Sequence; And That So Long As We Avoid Accepting As True What Is Not So, And Always Preserve The Right Order Of Deduction Of One Thing From Another, There Can Be Nothing Too Remote To Be Reached In The End, Or To Well Hidden To Be Discovered.

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.