The relations of Rousseau and Grimm understand two completely opposite periods: they meet in 1749 and become friendly. Their relations are “close”, and they are often diverted with certain Klupfell. A common taste for the music brings them closer. Rousseau introduces his/her friends to him, in particular Diderot, but it reproaches Grimm for not having never done anything in return. It undergoes the first treason of Grimm when this last hastens to tell in Therese Levasseur an inaccuracy of Rousseau.

As its successes, Grimm becomes more distant. It is par excellence the man of “parade”. He never did nothing but post feelings “that with less noise” Rousseau “had for him”. Following the “business of the Hermitage”, Rousseau is scrambled with his/her friend, become the lover of Mrs. d' Epinay, at the same time as with Diderot and the “holbachic coterie”. Grimm sends a furious letter of rupture to him. They will not be re-examined any more. Since then Grimm and Diderot would not have ceased plotting against Rousseau, in particular endeavouring to alienate the confidence of the Levasseur family to him.

However Grimm attentively follows the destiny and the productions of Rousseau which he comments on in his literary Correspondence. This magazine with confidential diffusion is sent only to the Princes and to the foreign sovereigns.

“I had one enough a large number of knowledge, but two only friends of choice, Diderot and Grimm. By an effect of the desire that I have to gather all that is expensive to me, I was too the friend from both so that they were not to it soon one of the other. I bound them; they were appropriate, and were linked between them even more narrowly than with me.”