If any one is inclined to regard this as superfluous, let him try the experiment of composing a play, and then writing the pantomime, or "business," for it; he will soon see what follies he commits.[257] Whatever we may think of the practice of writing the action as well as the words for the player, nobody would now dispute the wisdom of what Diderot says as to the part that pantomime fills in the highest kind of dramatic representation.

We must agree with his repeated laments over the indigence, for purposes of full and adequate expression, of every language that ever has existed or ever can exist.[258] "My dear master," he wrote to Voltaire on the occasion of a performance of _Tancred_, "if you could have seen Clairon passing across the stage, her knees bending under her, her eyes closed, her arms falling stiff by her side as if they were dead; if you heard the cry that she uttered when she perceives Tancred, you would remain more convinced than ever that silence and pantomime have sometimes a pathos that all the resources of speech can never approach."[259] If we wonder that he should have thought it worth while to lay so much emphasis on what seems so obvious, we have to remember that it did not seem at all obvious to people who were accustomed to the substitution of a mannered and symmetrical declamation for the energetic variety and manifold exuberance of passion and judgment in the daily lives of men.
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.