I only know one thing, and that is I know nothing

The years wrinkle our skin, but lack of enthusiasm wrinkles our soul.

There are beds and tables in the world - plenty of them, are there not? But there are only two ideas or forms of them - one the idea of a bed, the other of a table.

I am wiser than this man, for neither of us appears to know anything great and good; but he fancies he knows something, although he knows nothing; whereas I, as I do not know anything, so I do not fancy I do. In this trifling particular, then, I appear to be wiser than he, because I do not fancy I know what I do not know.

Do not grieve over someone who changes all of the sudden. It might be that he has given up acting and returned to his true self.

To use words and phrases in an easygoing manner without scrutinizing them too curiously is not in general a mark of ill-breeding. On the contrary, there is something low-bred in being too precise. But sometimes there is no help for it

Be true to thine own self.