Denis Diderot

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.

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

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.

All children are essentially criminal.

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

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

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.

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.

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

- Denis Diderot