The Development of Physical Influx in Early Eighteenth-Century Germany

Standard histories of modern philosophy(1) tend to view causality in the following way: After Descartes distinguishes between the mind and the body as two radically different kinds of substance, it becomes problematic as to how such substances could act on each other. Thus, Malebranche develops Occasionalism, which solves the problem by denying that any finite substance has any causal efficacy whatsoever, and Leibniz, dissatisfied with what he sees to be the perpetual miracles involved in the Occasionalist solution, develops Pre-established Harmony, according to which a substance can act, but only on itself. Hume, by inheriting an empiricist account of meaning, is then seen to criticize the very notion of causality insofar as it requires a necessary connection between cause and effect. Such histories typically end with Kant, who attempts to show the incoherence of Hume's critique in his Second Analogy of Experience. There are numerous difficulties with this picture. One is that Kant's contributions to the issue of causality are not exhausted by his reply to Hume in the Second Analogy, since Kant reacts to Leibniz in the Third Analogy as well as in other passages.(2) Another, related difficulty is;that on this picture Leibniz's Pre-established Harmony seems to have no effect on the rest of modern philosophy. This is simply wrong, and what makes it wrong is a philosophically interesting story, namely the development in early eighteenth-century Germany of a view Leibniz opposes to Pre-established Harmony and occasionalism and dubs influxus physicus or Influx.(3) Before the story can be told, however, some stage-setting is necessary. First, it is important to be clear about the most basic doctrines of Pre-established Harmony, Occasionalism, and Physical Influx.(4) Physical Influx asserts intersubstantial causation amongst finite substances.(5) For instance, when I appear to kick a ball, I really am the cause of the ball's motion. Pre-established Harmony denies intersubstantial causation, but affirms intrasubstantial causation. According to Pre-established Harmony, then, I am not the cause of the ball's motion, but rather the ball is simply causing itself to move (through the unfolding of its complete concept, in Leibniz's version). Occasionalism, like Pre-established Harmony, denies intersubstantial causation, but, unlike Pre-established Harmony, it denies intrasubstantial causation as well. Occasionalism typically asserts that God alone, that is, an infinite substance, is the cause of all changes, and thus of the ball's motion. Though there are other ways of defining these causal theories, this way has the advantage that the causal theories form an exhaustive disjunction.(6) Second, since I shall be focusing primarily on Pre-established Harmony and Physical Influx, it is worth considering Leibniz's reasons for rejecting Physical Influx and supporting Pre-established Harmony. Leibniz presents two main objections to Physical Influx. First, he repeatedly objects that physical influx is inconceivable because it is incomprehensible how one substance could act on another substance, that is, that an accident from one substance could be transferred or migrate to another substance.(7) Second, he argues that Physical Influx implies a violation of the laws of nature, more specifically, the law of conservation of motion. The idea is that if the mind were to act on the body so as to cause motion, then there would be more motion in the world after the mind's action on the body than beforehand, which is a clear violation of the law of the conservation of motion.(8) Leibniz develops a number of arguments for Pre-established Harmony. For example, in A New System of Nature he claims that Pre-established Harmony is at least possible, since God clearly has the power to endow a substance with an internal force that brings about all its later states. Moreover, it is also the most probable hypothesis because (1) Occasionalism requires perpetual miracles and Physical Influx encounters the aforementioned difficulties and (2) Pre-established Harmony has numerous advantages (for example, it displays our freedom, and the immortality of the soul and it allegedly provides a new proof for the existence of God). ...

Analogy · Causality (physics) · Empiricism · Epistemology · Harmony (color) · Meaning (existential) · Physics · Rest (music) · Classical Philosophy and Thought · Historical Philosophy and Science · Philosophy · Philosophy, Science, and History