IT WOULD BE HARD to overemphasize the importance of causation for the seventeenth century. In many respects, the topic exerts a kind of fascination over thought in this period. Like a leitmotiv, it appears constantly in philosophical discussions of the time. Many of these discussions discriminate at some length between various forms of causation. Often one form is stressed while another is denied. Yet, curiously enough, what we do not find anywhere is a complete denial of causation altogether. In light of David Hume's subsequent analysis of causation in A Treatise of Human Nature and the Enquiry concerning Human Understanding, this may seem a little odd, to say the least. The oddity is only increased by the fact that a number of seventeenth-century texts define the notion of a cause in terms that correspond quite closely to those of Hume. How exactly, then, are we to explain the fact that no one else appears inclined to deny causation completely? That such a possibility should simply not have occurred to anyone seems highly unlikely. Accordingly, there must be some other explanation for the universal adherence to some notion of a cause.
Among those associated with the Enlightenment interest in causation, one figure is normally not mentioned: Gottfried Wilhelm Leibniz. Instead, scholarship points to the absence of any serious definition of a cause in his oeuvre. The "windowless monads" are unable to receive impressions from external sources. Consequently, they cannot be affected by anything. As a result, it becomes meaningless to talk about causation in the normal sense. What we have is, rather, a "preestablished harmony" between different monads, arranged by an omniscient divine power that determines the experiences these monads have. The notion of a "preestablished harmony" allows Leibniz to reduce the existing universe to monads and their perceptions. But with a universe composed solely of monads and their perceptions, the problem of mind-body interaction is thereby eliminated. It has even been argued that a desire to eliminate the mind-body problem may have been what initially moved Leibniz to propose the scheme of a preestablished harmony. Since mind-body interaction entails the most serious causal difficulties, a