“Gestalt” is probably the best known contribution of Ehrenfels to philosophy and psychology. As Ehrenfels himself points out in his 1890 article “Über ‘Gestaltqualitäten’” (“On ‘Gestalt Qualities’”), he was inspired by a series of remarks in Ernst Mach’s 1886 book Beiträge zur Analyse der Empfindungen (Contributions to the Analysis of Sensations), in particular Mach’s claim that we would be able to sense spatial shapes and melodies (“tone shapes”) directly. Mach begins by discussing the comparison of geometrical shapes: “In examining two figures which are alike [gleiche Gestalten] but differently colored (for example, two letters of the same size and shape, but of different colors), we recognize their sameness of form [gleiche Form] at the first glance, in spite of the difference of color-sensation.” (Mach 1886, 43, translation from Mach 1914, 105, the same example can be found already in Stumpf 1883, 115, which Ehrenfels had read previously.)  However, Mach then also proceeds to apply the term Gestalt in a metaphorical sense to the qualitative moments of melodies. Gestalten, for Mach, appear thanks to an equality (Gleichheit) in the sensations, which can be noticed “at a glance”, i.e., they are given directly, not deduced or abstracted. Mach argues that the geometrical similarity of two whole figures would be given by the lower level equality of their elements (lengths, angles, etc.) (Mach 1886, 47; Mach 1914, 109). In analogy to his considerations about space, Mach also applies this analysis to time, finding the same “immediate” perception of Gestalt in rhythm and melody (Mach 1886, 128; Mach 1914, 285). In this way, Mach used the term Gestalt to indicate the characteristics of a whole that depend on the specific configuration of its parts. This formed one of the starting points for Ehrenfels’ much more focused discussions of Gestalten in 1890. The other starting point is of course the discussion in the School of Brentano about parts and wholes, “relations of relations” and higher order objects in general (in various terminologies). In particular, Ehrenfels’ teacher Alexius Meinong had dedicated a work specifically to the theory of relations (Meinong 1882), which is also repeatedly referred to by Ehrenfels, underscoring that relations are crucially important to his discussion and explicitly pointing out that relations themselves are nothing but Gestalt qualities (Ehrenfels 1890; Smith 1988, 101). At the same time, and due to more or less the same set of influences, Husserl also had used the term Gestalt and Gestaltmoment to indicate higher-order quasi-qualities and the unitary framework of the whole intuition (in a lecture from January 1890, see Husserl 2005, and in the 1891 Philosophy of Arithmetic, where he switches his terminology to “figural moment”). Despite such anticipations and parallels (see also the critical remarks by Zimmer in Albertazzi et al. 2001, 135 ff.), it was Ehrenfels’ work that thematized this whole topic and brought such diverse approaches into focus, thereby turning the psychology of Gestalten into a topic in its own right and fixating the terminology, problems, and scope of the debate about higher order objects and relations for the years to come.