The French language evolved considerably in the 18th century. Firstly, under the influence of science : all the words in – graphie, – logie , – isme are incorporated into the vocabulary. The sentence becoms shorter, gets rid of its excess qui, duquel, dequoi (compare with the style of Descartes for example in the seventeenth century). It becomes sentimental, with Rousseau. Witty and brilliant with Voltaire and Diderot. It looks a little more like the one we know today.
Breaking with the seventeenth century which, as you will recall, strove to create a pure language, free of popular words and phrases, the writers of the Enlightenment tend to believe that when faced with two similar words, there is not one bad and one good, but that each has its own nuance: the trick is to show finesse and accuracy.
Above all, French is asserting itself as a language of culture , as Latin or Greek were in Antiquity. In previous centuries, writers were often inclined to consider that although their language of expression was French, the real culture was Greek and Latin. Now there is more self-confidence and self-assurance in their minds. They are aware that they are doing more than scribbling comments in the margins of history. Their works have value and are those of a new time. Scientific progress and artistic productions are now most often associated with French.