Stendhal's _De l'Amour_, and in less degree his novels, have had to struggle for recognition, and the cause has largely been the peculiarity of his attitude--his scepticism, the exaggerated severity of his treatment of idyllic subjects, together with an unusual complement of sentiment and appreciation of the value of sentiment for the understanding of life. It is his manner of thinking, much rather than the strangeness of his thoughts themselves, which made the world hesitate to give Stendhal the position which it now accords him. But at least one great discovery the world did find in _De l'Amour_--a novelty quite apart from general characteristics, apart from its strange abruptness and stranger truth of detail. Stendhal's discovery is "Crystallisation"; it is the central idea of his book. The word was his invention, though the thought, which it expresses so decisively, is to be found, like most so-called advanced ideas, hidden away in a corner of Montaigne's Essays.[18] Crystallisation is the [Pg xviii] process by which we love an object for qualities, which primarily exist in our fancy and which we lend to it, that is to say, imaginary or unreal qualities. While Montaigne, and others no doubt, had seen in this a peculiarity of love, Stendhal saw in it love's essential characteristic--one might say, its explanation, if love were capable of being explained. Besides, in this book Stendhal is seeking the _how_ not the _why_ of love. And he goes beyond love: he recognises the influence of crystallisation upon other sides of life besides love. Crystallisation has become an integral part of the world's equipment for thought and expression.