The proof that you know ...

The proof that you know something is that you are able to teach it

The proof that you know something is that you are able to teach it

Quotes from the same author

It is the mark of an educated mind to be able to entertain a thought without accepting it.

Change in all things is sweet.

Well begun is half done.

In all things of nature there is something of the marvelous.

Happiness depends upon ourselves.