How Can You Be Certain

When I Consider This Carefully, I Find Not A Single Property Which With Certainty Separates The Waking State From The Dream. How Can You Be Certain That Your Whole Life Is Not A Dream?

If You Would Be A Real Seeker After Truth, It Is Necessary That At Least Once In Your Life You Doubt, As Far As Possible, All Things.

Intuition Is The Undoubting Conception Of A Pure And Attentive Mind, Which Arises From The Light Of Reason Alone, And Is More Certain Than Deduction.

I Suppose Therefore That All Things I See Are Illusions; I Believe That Nothing Has Ever Existed Of Everything My Lying Memory Tells Me. I Think I Have No Senses. I Believe That Body, Shape, Extension, Motion, Location Are Functions. What Is There Then That Can Be Taken As True? Perhaps Only This One Thing, That Nothing At All Is Certain.

If I Go For The Alternative Which Is False, Then Obviously I Shall Be In Error; If I Take The Other Side, Then It Is By... Chance That I Arrive At The Truth, And I Shall Still Be At Fault.... In This Incorrect Use Of Free Will May Be Found The Privation Which Constitutes The Essence Of Error.