The second factor, equally important, is that of good continuation and good shape. The things which we see have a better shape, are bounded by better… - Kurt Koffka

A complete theory would have to answer, among others, the following questions, given two adjoining retinal areas of different stimulation, under what conditions will the corresponding parts of the behavioural (perceptual) field appear of different whiteness but equal brightness (or "illumination"), when of different brightness but equal whiteness? A complete answer to this question would probably supply the key to the complete theory of colour perception in the broadest sense.

To apply the category of cause and effect means to find out which parts of nature stand in this relation. Similarly, to apply the gestalt category means to find out which parts of nature belong as parts to functional wholes, to discover their position in these wholes, their degree of relative independence, and the articulation of larger wholes into sub-wholes.

Things look as they do because of the field organization to which the proximal stimulus distribution gives rise. This answer is final and can be so only because it contains the whole problem of organization itself.