We have already seen that even when he wrote the Letter on the Deaf and Dumb, Diderot’s mind was exercised about gesture as a supplement to discourse.  In that Letter he had told a curious story of a bizarre experiment that he was in the habit of making at the theatre.  He used to go to the highest seats in the house, thrust his fingers into his ears, and then, to the astonishment of his neighbours, watch the performance with the sharpest interest.  As a constant playgoer, he knew the words of the plays by heart, and what he sought was to isolate the gesture of the performers, and to enjoy and criticise that by itself.  He kept his ears tightly stopped, so long as the action and play went well with the words as he remembered them, and he only listened when some discord in gesture made him suppose that he had lost his place.  The people around him were more and more amazed as they saw him, notwithstanding his stopped ears, shed copious tears in the pathetic passages.  “They could not refrain from hazarding questions, to which I answered coldly, ’that everybody had his own way of listening, and that my way was to stop my ears, so as to understand better’—­laughing within myself at the talk to which my oddity gave rise, and still more so at the simplicity of some young people who also put their fingers into their ears to hear after my fashion, and were quite astonished that the plan did not succeed."[260] This was an odd and whimsical way of acting on a conviction which lay deep in Diderot’s mind, namely, that language is a very poor, misleading, and utterly inadequate instrument for representing what it professes, and what we stupidly suppose it, to represent.  Rousseau had expressed the same kind of feeling when he said that definitions might be good things, if only we did not employ words in making them.

A curious circumstance is worth mentioning in connection with the Three Dialogues appended to The Natural Son.  Diderot informs his readers that the incidents of The Natural Son had actually occurred in real life, and that he knew the personages.  In the Dialogues it is assumed that the play had been written by the hero himself, and the hero is the chief speaker.  Not a word is said from which the reader would guess that Diderot had borrowed the substance of his plot and some of its least insipid scenes from Goldoni.  We can hardly wonder that he was charged with plagiarism.  Yet it was not deliberate, we may be sure.  When Diderot was strongly seized by an idea, outer circumstances were as if they did not exist.  He was swept up into the clouds.  “Diderot is a good and worthy man,” wrote Madame Geoffrin to the King of Poland, “but he has such a bad head, and he is so curiously organised, that he neither sees nor hears what he does see and hear, as the thing really is; he is always like a man who is dreaming, and who thinks all that he has dreamed quite real."[261]