Hume and Causal Inference

141 HUME AND CAUSAL INFERENCE Hume held that any time we reach by inference a belief about the existence or qualities of some object or event that we have not actually perceived, the inference is grounded in beliefs about causal relations holding between the object of belief and some other object or objects that have actually been experienced. I will examine here Hume's account of such causal inferences. There are many places in the Treatise of Human Nature at which Hume seems to claim that causal inferences take place when and only when the percipient has had an extensive previous experience of objects of the respective types as regularly conjoined in relations of contiguity and temporal priority. It seems to me that reliance on these passages alone gives a distorted view of Hume's theory of causal inference. Contrary to appearances, Hume did not hold that extensive previous experiences of objects of the same types as properly conjoined is either necessary or sufficient for causal inference. Hume's view is more subtle and complicated, and there are important considerations of coherence and holism present in it. Getting Hume's view on this matter clear is important because it shows how he can escape some of the objections that have been laid against his theory, and it makes possible a reading of Hume as a causal realist. Hume's theory of inference provides the resources for drawing a distinction between accidental and genuine causal regularities and it is compatible with the view that causal relations (and not mere de facto regularities) hold among events in the world independently of their being perceived. The examination begins by looking at a different, but related, issue. Why does Hume think 142 that of the three types of association, only cause and effect association is capable of producing belief? Hume puts the question in the form of a possible objection to his account. For it may be said, that if all the parts of that hypothesis be true, viz . that these three species of relation are deriv'd from the same principles; that their effects in inforcing and inlivening our ideas are the same; and that belief is nothing but a more forcible and vivid conception of an idea; it shou'd follow, that that action of the mind may not only be deriv'd from the relation of cause and effect, but also from those of contiguity and resemblance. But as we find by experience, that belief arises only from causation, and that we can draw no inference from one object to another, except they be connected by this relation, we may conclude, that there is some error in that reasoning, which leads us into such difficulties. (T 107) It is important to note that Hume is talking here only about beliefs about the existence or situations of objects that have not been intuited or experienced. Beliefs about relations of ideas (e.g. , that 2 + 2 = 4) are intuitions (or perhaps memories 2 of intuitions). Beliefs in the existence of things as experienced or in the previous existence of things as previously experienced automatically have the 3 vivacity of impressions or memory ideas. What Hume takes himself to need to explain is why cause and effect association allows for a transfer of this vivacity to an idea of an object or situation that has not itself been intuited or experienced and why 4 resemblance and contiguity association do not. If I see a green ball next to a red sweater, then I will normally subsequently believe that the green ball existed next to the red sweater at that time (at 143 least until my memories begin to lose vivacity). This is purely a matter of sense experience and memory. Now if I subsequently see a different red sweater (or the same sweater in a different location), I may be led to think of a green ball existing next to it purely through contiguity and resemblance association. But presumably I would not believe that a green ball existed next to the currently perceived red sweater unless I currently perceived a green ball or my belief was based on some 5 form of causal inference...