The general aim of my book has been but to point out a way in which a solution of these numerous problems (behavior and development) can be attained.… - Kurt Koffka

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.

Why We See Things and Not the Holes Between Them. We can now attempt an answer to the question why we do so. Two of the factors of organization which we have so far discussed seem to me to be the most important causes of this effect. In the first place, the segregation and unification which occurs will separate areas of different degrees of internal articulation, and according to our law, the more highly articulated ones will become figures, the rest fusing together to form the ground. Look at any landscape photograph. You see the shape of the things, the mountains, and trees and buildings, but not of the sky.

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.