  Ward attacks Leibniz’s reasoning at its very basis. Causal interaction was understood by Leibniz in terms of the doctrine of physical influx. On that model, direct causal interaction is rejected because properties cannot exist unless as inhering in substances; in passing from one substance to another, however, the communicated property would have to exist in a detached condition, which seems absurd. Could this simple piece of reasoning suffice to reject what we seem to experience all the time, namely our power to act directly upon external realities and to be immediately affected by them? In his answer to Leibniz, Ward remarks that the theory of physical influx categorizes the terms of a causal relation as substances to which qualities inhere; on this theory, even the monads are therefore conceived as if they were things. This involves a special sort of category-mistake: ‘Monads’—Ward says—“are conative, that is are feeling and striving subjects or persons in the widest sense, not inert particles or things” (260).