When we perceive complex structures such as spatial figures or melodies, what is it that we perceive? And what is the ontological status of such perceptual complexes? Until the 19th century Hume’s atomistic psychology still dominated the scene, according to which the perception of a complex can only be accounted for as a summation of simple perceptions, each having its own simple object. The central problem for such an account is to explain the characteristic unity of complexes that we perceive. Against the background of Ernst Mach’s attempt to solve this problem within the atomistic framework, by appeal to further sensations, ‘muscular sensations’ as he called them (“Bemerkungen zur Lehre vom räumlichen Sehen”, Zeitschrift für Philosophie und philosophische Kritik, N.F. 46, 1865: 1-5), the Austrian philosopher Christian von Ehrenfels presented a new proposal. Ehrenfels, a student of Franz Brentano, argued that we have to recognise special ‘Gestalt qualities’ of complexes of elementary data given in experience (Über Gestaltqualitäten, Vierteljahrsschrift für wissenschaftliche  Philosophie, 14, 1890: 242- 292). These Gestalt qualities are determined by the constituent elements of the associated complexes. But the Gestalt is not a whole  …

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