Music and painting are, materially speaking, very different arts. In the former a temporally presented mode of expression addresses itself to the ear, in the latter a spatially presented mode addresses itself to the eye, and they would not appear to admit of any comparison. Modern painting interfuses the dimensions of time and space, challenging the traditional distinctions between temporal and spatial arts. A kind of multi-dimensional art results. Gauguin and van Gogh believed that painting promised to become more like music. It has. Modern painting has entered a "musical" phase-- for the painter has turned composer and performer, and his works owe an obvious debt to the sister art. Music, in turn, has drawn from the painter's domain such material as bas considerably enriched the language of sound. In no previous age were they so interdependent, and this assertion is confirmed in the astonishing parallels between them before the First World War, when the notion of a relationship between painting and music was at its zenith. "Musicality" in modern painting is associated with a tendency towards abstraction. The nearer painting approaches a pictorial art which makes no specific reference to nature, the more nearly must it align itself with an autonomous and independent system such as music. Painting and music have come to share fundamental principles of organization. What makes a painting "musical"? A musical painter? So it would seem. A number of musicians and composers have abandoned promising musical careers in order to take up painting-- among them Ciurlionis, Klee, Feininger, Russolo, and Larry Poons. Other painters have deemed it necessary to acquire musical skills. Such painters as these were "musically" committed in their works: music instructed their visual sense and informed their expression. But not all modern painting could be described as "musical". “There are musical pictures, just as there are unmusical ones, pictures that are positively hostile to the whole notion of music.” (By the same token, there is also music "positively hostile to the whole notion of music, and consequently, to the whole notion of modern painting.) Some paintings which invite musical association are ambiguous and confusing. They may remind us of music, they may not. One cannot hear a painting or see music save in the experience of abnormal sensory agitation. However much synaesthetes would persuade us to the contrary, painting is not music. The relationship between painting and music is best explained in terms of their parallel developments, and in order to do this I have looked for corresponding gestures in the two arts. Painting arrived at abstraction by analogy with music (a useful ally, since music is fundamentally non-representational.) Before the First World War (and for a short while after) painters and composers were attuned to each other in a way that had few precedents in history: a strong bond was cemented between them, and there were a great many areas in which they met. All subsequent developments in painting and music refer, in some way, to the innovations and inventions of the musical phase of modern painting.