I Can Doubt Everything, Except One Thing,

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.

And Thereby Make Ourselves, As It Were, The Lords And Masters Of Nature.

I Should Consider That I Know Nothing About Physics If I Were Able To Explain Only How Things Might Be, And Were Unable To Demonstrate That They Could Not Be Otherwise.

For To Be Possessed Of A Vigorous Mind Is Not Enough; The Prime Requisite Is Rightly To Apply It.

What Then Is The Source Of My Errors? They Are Owing Simply To The Fact That, Since The Will Extends Further Than The Intellect, I Do Not Contain The Will Within The Same Boundaries; Rather, I Also Extend It To Things I Do Not Understand. Because The Will Is Indifferent In Regard To Such Matters, It Easily Turns Away From The True And The Good; And In This Way I Am Deceived And I Sin.