Denis Diderot

The number of books will grow continually, and one can predict that a time will come when it will be almost as difficult to learn anything from books as from the direct study of the whole universe. It will be almost as convenient to search for some bit of truth concealed in nature as it will be to find it hidden away in an immense multitude of bound volumes.

There is no moral precept that does not have something inconvenient about it.

Watch out for the fellow who talks about putting things in order! Putting things in order always means getting other people under your control.

There are three principal means of acquiring knowledge. . . observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination.

Our observation of nature must be diligent, our reflection profound, and our experiments exact. We rarely see these three means combined; and for this reason, creative geniuses are not common.

Genius is present in every age, but the men carrying it within them remain benumbed unless extraordinary events occur to heat up and melt the mass so that it flows forth.

All children are essentially criminal.

I can be expected to look for truth but not to find it.

Only passions, great passions, can elevate the soul to great things.

A thing is not proved just because no one has ever questioned it. What has never been gone into impartially has never been properly gone into. Hence scepticism is the first step toward truth. It must be applied generally, because it is the touchstone.