The proof of the theory of the limits of the arts has been credited to Lessing, but his merit should rather be limited to having been the first to draw attention to the problem. His solution was false, but his achievement nevertheless great, in having posed the question clearly. No one before him, in antiquity, in the Middle Age, or in modern times, had seriously asked: What is the value of the distinctions between the arts? Which of them comes first? Which second? Leonardo da Vinci had declared his personal predilection for painting, Michael Angelo for sculpture, but the question had not been philosophically treated before Lessing. Lessing's attention was drawn to the problem, through his desire to disprove the assertions of Spence and of the Comte de Caylus, the former in respect to the close union between poetry and painting in antiquity, the latter as believing that a poem was good according to the number of subjects which it should afford the painter. Lessing argued thus: Painting manifests itself in space, poetry in time: the mode of manifestation of painting is through objects which coexist, that of poetry through objects which are consecutive. The objects which coexist, or whose parts are coexistent, are called bodies. Bodies, then, owing to their visibility, are the true objects of painting. Objects which are consecutive, or whose parts are consecutive, are called, in general, actions. Actions, then, are the suitable object of poetry. He admitted that painting might represent an action, but only by means of bodies which make allusion to it; that poetry can represent bodies, but only by means of actions. Returning to this theme, he explained the action or movement in painting as added by our imagination. Lessing was greatly preoccupied with the naturalness and the unnaturalness of signs, which is tantamount to saying that he believed each art to be strictly limited to certain modes of expression, which are only overstepped at the cost of coherency. In the appendix to his _Laocoön_, he quotes Plutarch as saying that one should not chop wood with a key, or open the door with an axe. He who should do so would not only be spoiling both those utensils, but would also be depriving himself of the utility of both. He believed that this applied to the arts. The number of philosophers and writers who have attempted empirical classifications of the arts is enormous: it ranges in comparatively recent times from Lessing, by way of Schasler, Solger, and Hartmann, to Richard Wagner, whose theory of the combination of the arts was first mooted in the eighteenth century.