He uses a thought-experiment to derive the mathematical expression of the basic laws of representational “motion”, that is, the laws according to which our mental representations interact with each other. Under normal conditions, representations are of different strengths, and so oppose each other with differential intensity, making a clear statement of their underlying laws difficult. Herbart therefore first considers an ideal case, the extreme at which two representations are “fully opposed” one to another, that is, one is completely inhibited, so that the other may remain unconstrained (PsW: 139). Under such circumstances, 