Yet a problem remains, namely whether Gestalt qualities arise as a result of some activity on our part when confronted with the relevant complex of elements or without any contribution of the intellect. Mach held the latter view, that “Gestalten are objects of ‘sensation’ just as soon as their respective foundations are given to consciousness” (Ehrenfels 1890; Smith 1988, 111). Ehrenfels points out first of all that Gestalten are not always noticed (e.g. proverbially seeing the trees but not the forest) and some effort seems to be required in grasping a shape by filling out and complementing the Gestalt suggested by the foundations, e.g. when “seeing” the third dimension suggested by the cues of a perspectival drawing (Ehrenfels 1890; Smith 1988, 111 ff.). While we do not actually generate the Gestalt in a separate act, specifically meant to add it to the foundation, we do expend effort in completing the required set of presentational elements needed for the Gestalt, which then arises spontaneously. This, however, does not exclude that different Gestalten may supervene on the same foundations and that we can switch between them by changing the focus of our attention. By bringing a different complex of presentational elements into the foreground, i.e., by varying the foundations, we can also (indirectly) vary the Gestalt (Ehrenfels 1890; Smith 1988, 112 ff.).