The admirable Salons were not Diderot's only contributions to aesthetic criticism. He could not content himself with reproductions, in eloquent language upon paper, of the combinations of colour and form upon canvas. No one was further removed from vague or indolent expansion. He returns again and again to examine with keenness and severity the principles, the methods, the distinctions of the fine arts, and though he is often a sentimentalist and a declaimer, he can also, when the time comes, transform himself into an accurate scrutiniser of ideas and phrases, a seeker after causes and differences, a discoverer of kinds and classes in art, and of the conditions proper to success in each of them. In short, the fact of being an eloquent and enthusiastic critic of pictures, did not prevent him from being a truly philosophical thinker about the abstract laws of art, with the thinker's genius for analysis, comparison, classification. Who that has read them can ever forget the dialogues that are set among the landscapes of Vernet in the Salons of 1767?[53] The critic supposes himself unable to visit the Salon of the year, and to be staying in a gay country-house amid some fine landscapes on the sea-coast. He describes his walks among these admirable scenes, and the strange and varying effects of light and colour, and all the movements of the sky and ocean; and into the descriptions he weaves a series of dialogues with an abbe, a tutor of the children of the house, upon art and landscape and the processes of the universe. Nothing can be more excellent and lifelike: it is not until the end that he lets the secret slip that the whole fabric has been a flight of fancy, inspired by no real landscape, but by the sea-pieces sent to the exhibition by Vernet. [53] xi. 98-149. This is an illustration of the variety of approach which makes Diderot so interesting, so refreshing a critic. He never sinks into what is mechanical, and the evidence of this is that his mind, while intent on the qualities of a given picture, yet moves freely to the outside of the picture, and is ever cordially open to the most general thoughts and moods, while attending with workmanlike fidelity to what is particular in the object before him.[54] [54] _E.g._ xi. 223.