 Perception has already been discussed briefly above. But it will be advisable to consider also a definition from a letter to Des Bosses (and echoed in many other passages) in which Leibniz discusses perception as the representation or “expression” of “the many in the one” (letter to Des Bosses, 11 July 1706; G II, 311). We shall return to this definition below. Appetitions are explained as “tendencies from one perception to another” (Principles of Nature and Grace, sec.2 (1714); G VI, 598/A&amp;G 207). Thus, we represent the world in our perceptions, and these representations are linked with an internal principle of activity and change (Monadology, sec.15 (1714); G VI, 609/A&amp;G 215) which, in its expression in appetitions, urges us ever onward in the constantly changing flow of mental life. More technically explained, the principle of action, that is, the primitive force which is our essence, expresses itself in momentary derivative forces involving two aspects: on the one hand, there is a representative aspect (perception), by which the many without are expressed within the one, the simple substance; on the other, there is a dynamical aspect, a tendency or striving towards new perceptions, which inclines us to change our representative state, to move towards new perceptions. (For more details, see Carlin 2004 and Jorati 2017.)