Why think that substances express their causes?

[Cross-posted from modsquad.]

Leibniz thought (at least sometimes) that substances express God, because they express their causes. But why did he think that substances express their causes? In this post I briefly explore three ways in which we might try to understand his reasons for this.

Version 1: expression and knowledge

The late-1670s note “What is an idea?” (L 207-8, A 6.4.1369-71) provides some possible illumination. In the course of his discussion Leibniz notes that “every entire effect represents the whole cause, for I can always pass from knowledge of such an effect to knowledge of its cause” (L 208). So if we have knowledge of an “entire effect” then we will be able to acquire knowledge of the “whole cause” of that effect. That seems to suggest this argument.

  1. If one has knowledge of an (entire) effect, one can acquire knowledge of its (whole) cause.
  2. That could only be the case if the effect represented the cause. So
  3. All (entire) effects represent their (whole) causes.

Some details about ‘entire’ and ‘whole’ aside, this gets us close to the Discourse’s claim that effects express their causes. Moreover, premise 1 might gain some motivation from widespread views of knowledge and understanding that adhere to or approximate the slogan that to know is to know through causes. On the other hand, this seems not tell us why effects express their causes, even if it does show us that it must be the case that they do. Moreover, this is a text from several years before the Discourse, and it is not so clear that the details of Leibniz’s views of expression (in particular, expression of God) were all that stable over time.

Version 2: the cause-effect relation as a special case of expression

Dan Garber discusses expression in his Leibniz: Body, Substance, Monad (216-24). Among other things, he argues that “The cause/effect relation is a special case of the expression relation” (218) (basically because expression requires a “constant and fixed” relationship, and causation is such a relationship).

Thinking along this sort of line, we might construct another argument for the claim that effects express their causes.

  1. The relation of expression holds between two things, A and B, when there is a regular relation between them.
  2. The cause-effect relation is an regular relation between two things. So
  3. When two things stand in the cause-effect relation, the relation of expression also hold between them. So
  4. All effects express their causes.

Evaluating this is largely going to be a matter of deciding whether causation is indeed among the ‘regular’ relations that Leibniz says are required for expression. It doesn’t seem to be one of Leibniz’s usual examples. (Though he does, as in DM15, attempt to explain apparent causal relationships, as between two finite substances, in terms of expression.) On the other hand, the expression of God is not a usual example of expression either.

Version 3: expression and complete concepts

There are yet other Leibnizian reasons to think that an effect will express its cause, if one focuses on the Discourse. Indeed we can I think find a complete Leibnizian reason for the view in the Discourse itself.

Consider in particular the views expressed in DM 8 (about complete concepts, etc). There will be true claims of the form ‘S is P’ that relate any substance to God. Suppose for instance that ‘P’ is ‘ultimately an effect of God’. For any created substance this will be true. Thus, by the view about concepts explained in DM 8, ‘ultimately an effect of God’ will be part of the complete concept of every substance. And, indeed, there will be marks and traces in each substance corresponding to this predicate. So we can at least say that each substance represents God. Though we are some distance from talk of functions and isomorphisms, we are, given that expression more or less is representation, at a point at which we might see why Leibniz would say that all substances express God. Thus, we could understand the view that all substances express their causes as a consequence of other Leibnizian views about substances and language.

The importance of expressing causes might appear to be minimal on this reading: substances turn out to express causes simply because they express everything that stands in any relation to them (not just a regular one, whatever that is). On the other hand, as a reading of the Discourse, or or Leibniz’s views in 1686, this approach has the (slight?) advantage that the resources for explaining why Leibniz thought that substances express their causes are contained in the text itself. This being the reason also fits nicely with the view (that all individual substance express God) being present in Leibniz’s “Primary Truths” essay, which attempts to ground many Leibnizian views in his views about language. And it might also help explain why the expression of God is not a persistent feature of Leibniz’s statements about substances — as the DM8 view tends to disappear, this view of all substances as expressing God might naturally tend to disappear with it.