of the parlour or the country walk did not mean in Diderot's case the
empty fluency and nugatory emphasis of the ordinary talker of
reputation. It must have been both pregnant and copious; declamatory in
form, but fresh and substantial in matter; excursive in arrangement, but
forcible and pointed in intention. No doubt, if he was a sage, he was
sometimes a sage in a frenzy. He would wind up a peroration by dashing
his nightcap passionately against the wall, by way of clencher to the
argument. Yet this impetuosity, this turn for declamation, did not
hinder his talk from being directly instructive. Younger men of the most
various type, from Morellet down to Joubert, men quite competent to
detect mere bombast or ardent vagueness, were held captive by the
cogency of his understanding. His writings have none of this compulsion.
We see the flame, but through a veil of interfused smoke. The expression
is not obscure, but it is awkward; not exactly prolix, but heavy,
overcharged, and opaque. We miss the vivid precision and the high
spirits of Voltaire, the glow and the brooding sonorousness of Rousseau,
the pomp of Buffon. To Diderot we go not for charm of style, but for a
store of fertile ideas, for some striking studies of human life, and for
a vigorous and singular personality.

Diderot's knowledge of our language now did him good service. One of
the details of the method by which he taught himself English is curious.
Instead of using an Anglo-French dictionary, he always used one in
Anglo-Latin. The sense of a Latin or Greek word, he said, is better
established, more surely fixed, more definite, less liable to capricious
peculiarities of convention, than the vernacular words which the whim or
ignorance of the lexicographer may choose. The reader composes his own
vocabulary, and gains both correctness and energy.[25] However this may
be, his knowledge of English was more accurate than is possessed by most
French writers of our own day. Diderot's first work for the booksellers