We have to remember then that Diderot was in this respect of the Socratic type, though he was unlike Socrates, in being the disseminator of positive and constructive ideas.  His personality exerted a decisive force and influence.  In reading the testimony of his friends, we think of the young Aristides saying to Socrates:  “I always made progress whenever I was in your neighbourhood, even if I were only in the same house, without being in the same room; but my advancement was greater if I were in the same room with you, and greater still if I could keep my eyes fixed upon you."[24] It has been well said that Diderot, like Socrates, had about him a something daemonic.  He was possessed, and so had the first secret of possessing others.  But then to reach excellence in literature, one must also have self-possession; a double current of impulse and deliberation; a free stream of ideas spontaneously obeying a sense or order, harmony, and form.  Eloquence in the informal discourse 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 after his marriage seems to have been a translation in three volumes of Stanyan’s History of Greece.  For this, to the amazement of his wife, he got a hundred crowns.  About the same time (1745) he published Principles of Moral Philosophy, or an Essay of Mr. S. on Merit and Virtue.  The initial stands for Shaftesbury, and the book translated was his Inquiry concerning Virtue and Merit.