Uncertainty is an uncomfortable position, but certainty is an absurd position.

By three methods we may learn wisdom: First, by reflection, which is noblest; Second, by imitation, which is easiest; and third by experience, which is the bitterest.

There is more intelligence in your body than in your best wisdom.

Discovery consists of seeing what everybody has seen and thinking what nobody has thought.

I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived. I did not wish to live what was not life, living is so dear; nor did I wish to practise resignation, unless it was quite necessary. I wanted to live deep and suck out all the marrow of life, to live so sturdily and Spartan-like as to put to rout all that was not life, to cut a broad swath and shave close, to drive life into a corner, and reduce it to its lowest terms, and, if it proved to be mean, why then to get the whole and genuine meanness of it, and publish its meanness to the world; or if it were sublime, to know it by experience, and be able to give a true account of it in my next excursion.

I shall never cease from the practice and teaching of philosophy, exhorting anyone whom I meet after my manner, and convincing him, saying: O my friend, why do you who are a citizen of the great and mighty and wise city of Athens, care so much about laying up the greatest amount of money and honor and reputation, and so little about wisdom and truth and the greatest improvement of the soul, which you never regard or heed at all? Are you not ashamed of this? And if the person with whom I an arguing says: Yes, but I do care: I do not depart or let him go at once; I interrogate and examine and cross-examine him, and if I think that he has no virtue, but only says that he has, I reproach him with overvaluing the greater, and undervaluing the less. ...For this is the command of God, as I would have you know...