In the psychological fields most fundamental to the whole behavior of living things the transition seems inevitable to a Galileian view of dynamics, which derives all its vectors not from single isolated objects, but from the mutual relations of the factors in the concrete whole situation, that is, essentially, from the momentary condition of the individual and the structure of the psychological situation. The dynamics of the processes is always to be derived from the relation of the concrete individual to the concrete situation, and, so far as internal forces are concerned, from the mutual relations of the various functional systems that make up the individual.

p. 41; partly cited in: Kay Deaux, Mark Snyder (2012) The Oxford Handbook of Personality and Social Psychology. p. 74 - A Dynamic Theory of Personality, 1935