To imitate the laborious literary search of Bayle or of Brucker, and to attempt to compile an independent history of philosophy, would have been to sacrifice the Encyclopaedia as a whole, to the superfluous perfection of a minor part.
There is only one imperative condition in such a case, namely, that the writer should pass the accepted material through his own mind before reproducing it.

With this condition it was impossible for a man of Diderot's indefatigable energy of spirit, not as a rule to comply.
But this rule too had exceptions.

There were cases in which he reproduced, as any mere bookmaker might have done, the thought of his authority, without an attempt to make it his own.

Of the confusion and inequalities in which Diderot was landed by this method of mingling the thoughts of other people with his own, there is a curious example in the two articles on Philosopher and Philosophy.

In the first we have an essentially social and practical description of what the philosopher should be; in the second we have a definition of philosophy, which takes us into the regions most remote from what is social and practical.