It Ain't Necessity, so . . . (With Apologies to George Gershwin)

IT AIN'T NECESSITY, SO . . . (With Apologies to George Gershwin) I shall argue in this paper that what Hume calls the idea of necessary connection is mislabelled, and that what he ought to call the idea of necessary connection is not so labelled. My argument is not that there are, on Hume's view, real necessary connections between causes and their effects but rather that there is an idea of genuine necessary connection — what I call logical necessity — which we all mistakenly believe extends to causal connections. The genesis of this mistake is given a psychological explanation in the Treatise. Precisely how does Hume account for the origin of what he calls our idea of necessary connection? I have argued elsewhere that, whatever the answer, it has little philosophical importance. My reason was that, given Hume's view that causal connections are not necessary, the question must be viewed as one within psychology. Recent work on Hume, however, has convinced me that my former opinion was much too quick. Imlay, for example, has challenged Hume's distinction between demonstrative and probable inference on the grounds that Hume gives only one account of necessity for both 2 mathematical and lawlike truths. As I now see much more clearly, there are important philosophical distinctions that must be made in any full explication of Hume's view of the origin of our idea of causal necessity. I shall attempt an answer to the lead question of the second paragraph. My strategy is as follows. I shall first present a synopsis of Hume's account of our belief in causal necessity. Next, I shall develop 87. 88. a view of logical necessity. Finally, I shall briefly examine the exact genesis of the confusion between logical and causal necessity. Consider the following three propositions: (1)Hume does not believe that there are necessary causal connections. (2)All statements of laws of nature are on Hume's view descriptions of constant conjunctions, the logical form of which is captured by the Russellian " (x) [fx => gx]." (3)This logical form captures Hume's first definition of "cause." On these three propositions I and many other philosophers agree. I and an ever-shrinking number of philosophers also believe that Hume is right. But everyone, according to Hume, in some sense believes that causal connections are necessary; the Humean philosopher knows they are not but acts otherwise, while the ordinary person simply acts without the knowledge. Since everyone believes what is false, only a psychological explanation can be given for why we believe it anyway. Thus, Hume's second definition of "cause", and the view that the idea of necessity arises from the determination of the mind to pass from the impression of a cause to an idea of 3 its effect. The three most salient passages from the Treatise on the production of the idea of necessary connection follow. As we shall see, these passages cannot be understood without considering a number of others. For after a frequent repetition, I find, that upon the appearance of one of the objecte , the mind is determin 'd by custom to consider its usual attendant, and to consider it in a stronger light upon account of 89. its relation to the first object. 'Tis this impression, then, or determination, which affords me the idea of necessity . (T 156) Tho ' the several resembling instances , which give rise to the idea of power, have no influence on each other, and can never produce any new quality in the object, which can be the model of that idea, yet the observation of this resemblance produces a new impression in the mind, which is its real model. For after we have observ 'd the resemblance in a sufficient number of instances , we immediately feel a determination of the mind to pass from one object to its usual attendant, and to conceive it in a stronger light upon account of that relation. This determination is the only effect of the resemblance; and therefore must be the same with power or efficacy , whose idea is deriv 'd from the resemblance . The several instances of resembling conjunctions leads us into the notion of power and necessity .... Necessity , then...