Abstract

The mature Leibniz often describes monads as having two types of modifications: perceptions and appetites. But why would monads need appetites? When reading secondary literature about Leibniz, it can easily look as if appetites are superfluous: some scholars describe the inner workings of monads without saying much, if anything, about appetites. Instead, they focus on perceptions and explain the transition to new perceptions by reference to prior perceptions together with the underlying primitive force or law of the series. These interpretations appear to be doing just fine without invoking appetites. And, in fact, there are texts in which Leibniz himself neglects appetites almost completely. Some passages suggest that perceptions cause other perceptions, and other texts indicate that the monads themselves cause perceptions directly. If that is the case, it is not clear what purpose appetites serve; they do not appear to be needed for explaining monadic change. One possible response to the question why monads need appetites is the following. Appetites, according to Leibniz, are monadic tendencies to transition to new perceptions. Perhaps without such tendencies, no change would occur in a monad. On this interpretation, a full explanation of monadic change needs to invoke tendencies, and those in turn are (or include) appetites. I think that this response is partially correct, as I will argue later. Yet, it does not fully explain the function of appetites. How precisely are appetites (viewed as tendencies) supposed to figure into the explanation—do they function as causes of change, and if so, what kinds of causes? Are they efficient, final, or formal causes, or perhaps causes of yet another type? Or might they figure into the explanation in some non-causal way? This paper explores possible answers to the question what role appetites play in the lives of monads. There is not enough time to discuss these answers in much detail or exhaust the logical space, but I will briefly consider the options that strike me as the most promising contenders. These options are: (1) appetites are superfluous; there is no sense in which they explain or cause monadic change; (2) appetites are formal causes; (3) appetites are final causes; (4) appetites are efficient causes; (5) appetites are ultimately the same as perceptions (or aspects of perceptions), and perceptions in turn cause or explain monadic change; and (6) appetites are not causally involved in monadic change, but they are explanatory in a loose, derivative sense. I will argue for a version of the last option. The resulting picture of monadic change is admittedly radical and strange but there are excellent reasons to embrace it.