“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.”

At last I will devote myself sincerely and without reservation to the general demolition of my opinions.

I had become aware, as early as my college days, that no opinion, however absurd and incredible can be imagined, that has not been held by one of the philosophers.

To know what people really think, pay attention to what they do, rather than what they say.

Let whoever can do so deceive me, he will never bring it about that I am nothing, so long as I continue to think I am something.

Am I so tied to a body and senses that I am incapable of existing without them?

Each problem that I solved became a rule which served afterwards to solve other problems.

The first precept was never to accept a thing as true until I knew it as such without a single doubt

Masked, I advance.

There is nothing more ancient than the truth.

When it is not in our power to determine what it true, we ought to follow what is most probable.

For I found myself embarrassed with so many doubts and errors that it seemed to me that the effort to instruct myself had no effect other than the increasing discovery of my own ignorance

All that is necessary to right action is right judgment, and to the best action the most correct judgment.

I desire to live in peace and to continue the life I have begun under the motto ‘to live well you must live unseen’.

Truths are more likely to have been discovered by one man than by nation

I doubt, therefore I think, therefore I am.

But what then am I? A thing that thinks. What is that? A thing that doubts, understand, affirms, denies, wills, refuses, and that also imagines and senses.

Who knows most, doubts most; entertaining hope means recognizing fear.

I cannot love thee; thou ‘rt worse than thy brother. Go, say thy prayers, child, and ask God’s pardon. I doubt thy mother and I must rue that we ever reared thee!

In these days, it is doubtful that any child may reasonably be expected to succeed in life if he is denied the opportunity of an education.

Individuals sometimes feel insignificant and doubt that one person can really make a difference in this world. Well, believe me, one person can.

You know, failure hurts. Any kind of failure stings. If you live in the sting, you will – undoubtedly – fail. My way of getting past the sting is to say no, I’m just not going to let this get me down.

Our grand business undoubtedly is, not to see what lies dimly at a distance, but to do what lies clearly at hand.

It was essential that I never show doubt about what I was doing.

When the mind once allows a doubt to gain entrance, the value of deeds performed grow less, their character changes, we forget the past and dread the future.