On this weblog I have been dribbling out bits of the causal theory of Lady Mary Shepherd (1777-1847). Here's a bit of recap to give a taste of how it fits together.
At the heart of Shepherd's causal theory is reflection on the causal principle, namely, that every beginning of existence has a cause. Her full analysis of our development and application of this principle is something like this:
1. A new quality appears to my senses.
2. New qualities are differences; and thus the appearance of a new quality is the introduction of a difference; the introduction of a difference is causation.
3. This new quality could not be caused by itself (it would not then be an introduced difference).
4. In the environment of this new quality there are not any surrounding objects except such-and-such object(s) that could affect it.
5. Therefore such-and-such occasioned it, because there is nothing else to make a difference and a difference cannot begin of itself (3 and 4).
She notes that this sort of reasoning is standard in scientific work, and insists that one trial is all that is necessary to establish the general principle. If she is right about this, then, as she rightly notes, Hume would be wrong in his claim that the causal principle is based on custom. All we actually need in practice, Shepherd thinks, is to reason on a single case involving an introduction of a difference; this serves as an occasion adequate for our deriving the general principle, which is, if she is right, necessary.
(3) is a significant move in the analysis, so it is worthwhile to look more closely at her reasoning on this point. Suppose we have an object that 'begins its existence of itself', i.e., just begins, uncaused. This beginning of an object is "an action, which is a quality of an object not yet in being, and so not possible to have its qualities determined, nevertheless exhibiting its qualities". In other words, she thinks "beginning to be, uncaused" involves a contradiction; beginning to be is necessarily an introduction of a difference, and therefore requires something from which it may be introduced. As she puts it elsewhere, objects cannot begin their existences except as having the nature of effects.
This is perhaps made clearer by the way she thinks differences are usually introduced. Shepherd sees causation as a "mixture of qualities." Suppose you have a cause (C) and an object (O) or co-cause. Each of these has a number of properties or qualities. When C acts on O (or combines with O), the qualities 'mix'. The mixed result is the effect. So, for instance, I punch my fist into clay, the resulting impression is a 'mixture' of some of the properties of my fist and some of the properties of the clay.
Take another example, which will perhaps give a clearer idea of the significance of the view. There is a book on a sturdy table. That the book does not fall through the table is necessitated by the combined properties of the book and the table. It is not impossible, of course, for books to fall through tables; but it is only possible if some of the properties of either the book, or the table, or both, are changed. That is, a change can be induced in the situation only by introducing new properties into the mix. These new properties are causes of new situations. On this view of causation, the causal principle is necessary, because every change of properties requires the introduction of new properties. On the mixture view of causation, Shepherd thinks, anything new is necessarily an effect of a new introduction of properties. This, of course, is exactly right; you can't change the properties of a situation without changing its properties; if you have a new set of properties, it can only be because some properties in the set are new.
Shepherd, always very perceptive as to the implications of her positions, notes that this means that cause and effect, properly speaking, are simultaneous. If causation is the introduction of difference, and effect is the beginning of existence of the introduced difference, cause and effect are strictly occurring at the same time. They entail each other, and therefore cannot be separated by an interval. Likewise, she notes that on her view one can often call the same thing 'cause' or 'effect' depending on how you look at it. For instance, the entire set of properties involved in the interaction can be regarded either as the effect (given that it is newly different because some of its properties are newly different) or as cause (given that it is the whole set of properties in union that makes the new difference). This means that Shepherd's causal theory has an immense capacity to capture the various ways we actually do tend to use the words 'cause' and 'effect'.
This is all very rough; Shepherd has been unduly neglected, and, indeed, has been virtually ignored. Nonetheless there is an astounding amount of interesting analysis in her work, and I hope this brief, rough summary is enough to intrigue people into looking at her a bit.
(Cross-posted to Houyhnhnm Land.)