In many of his comments on his art, both painting and sculpture, Matisse makes clear that he is concerned not with detail but with picking out elements of the model that correspond to his vision and then finding a purely sculptural or painterly form that conveys in a heightened way his feeling for it. Sarah Stein, a pupil at the academy run by Matisse in Paris from 1908-11 recorded him saying that an 'undecided, indefinite' form cannot express what the artist sees: 'Therefore, exaggerate according to the definite character for expression ... The model must not be made to agree with a preconceived theory or effect. It must impress you, awaken in you an emotion, which you in turn seek to express.'
Matisse's series 'Back I-IV' perfectly reflects this approach for in it can be traced, in one of the most extraordinary sculptural series of the twentieth century, the evolution of his vision of the formal structure and the emotional significance of the female back. This subject, it is worth noting, had been a major preoccupation of C?zanne, one of Matisse's artistic heroes, in his late paintings of bathers. The first 'Back' was made by Matisse about 1909-10 and shows a chunky, forceful emphasis on the main muscles of the model. The pose with one arm around the head and the other by the side is compact, the arm on the right side to some extent balanced by the prominent breast seen on the left. The rest of the series shows a progressive simplification towards the massive, primitive unity of the final version made in 1930 [Tate Gallery T00082].
Simon Wilson, Tate Gallery: An Illustrated Companion, Tate Gallery, London, revised edition 1991, p.152