David Hume, the 18th century Scottish philosopher, made several lasting contributions to Western Philosophy. The following will address one such contribution: the notion of the uncertainty of that which unites a cause with its effect as presented in Hume’s Inquiry Concerning Human Understanding, 7:1. It will be shown, first, that Hume’s epistemology takes sense perception as its point of departure, and in consequence of this, secondly, that Hume is unable to affirm that the connection between an effect and its cause is necessary. Third, we will explore Hume’s argument that the common escape route for this problem—the positing of a god for the connection between a cause and an effect—is unsatisfactory.
Hume begins by noting that there is a certain epistemic disparity between the ‘mathematical’ and the ‘moral’ sciences. The mathematical sciences deal with sense-realities, and our ideas of them are therefore quite definite and exact. The moral sciences, on the other hand, do not allow the possibility of as definite and exact idea to be formed with regard to its subject matter. The reason for this is due to the fact that neither moral notions, nor the functioning of the intellect, nor the behavior of the passions are readily perceived by the senses.
On the other hand, Hume continues, each of these sciences has a disadvantage peculiar to itself. When one realizes this, one realizes that it may well be the case that these distinct sciences are on equal footing from an epistemic point of view. For example, the higher ideas of math are rather complex and not immediately perceptible; moral precepts, on the other hand, seem to be inferred with relative ease. Hence each discipline has its own problem of obscurity.
Hume then goes on to claim that all of our ideas are representations of impressions. This claim is important in light of what follows, for it is precisely this epistemic doctrine which explains the problem that Hume will later discover with regard to causation. If the source of ideas are only impressions (i.e., mental representations of sense perceptions, and the recalling of our own mental processes and emotions), then it necessarily follows that anything that is not an impression in this sense cannot qualify as being an idea, and therefore, cannot be known with an adequate level of certainty.
If a phenomenon or an idea seems obscure to me, I have access to a means whereby I can remedy this situation: the re-presentation of the impression. If, for example, my idea of the form of the chair I’m sitting on seems obscure, I can re-actualize the impression of the chair, thus arriving at a more definite idea. But what of those things which are opaque to the senses, and not immediately experienced by the mind?
Hume chooses the notion of causation, or “necessary connection,” to further assess this problem. He begins by attempting to re-present to the mind various impressions with which the phenomenon of causation is associated, and in doing so, it becomes immediately apparent that we have no direct perception of that power which joins a cause to its effect. Coldness always follows ice, and hotness always follows fire, but in neither case is this connection between the one and the other perceptible: there is nothing in the form of an icicle that necessarily suggests coldness, nor is heat deducible from the form of a flame.
Causation, therefore, is not a notion that is justified by sense experience. However, we are—so it seems—directly aware of one manner in which a cause is related to its effect, and to find this, we need only look inside of ourselves. If I desire to type this essay, I sit down and begin typing the words which seem to me to be appropriate for the fulfillment of this task. In other words, I will to type the word “causation,” and my limbs immediately produce the word on the computer screen by tapping the necessary buttons on the keypad. In this case, the cause (i.e., my willing) would seem immediately connected to the effect (i.e., the actualization of my will). Therefore, it would seem that our notion of necessary connection is justified via the recollection of our own mental processes.
Yet this seeming certainty is actually superficial, for when we will to bring about a state of affairs, we are wholly unaware of the power which is responsible for its realization. For example, I can immediately recall to my mind the act of willing to type the word “causation,” but the that which connects my willing to type the word, and the typing of the word itself, remains wholly opaque. For in the first place, the connection between the mind and the body is obscure. Second, it is more than intriguing that our will cannot control all members of our body (e.g., though I move my right leg by willing to do so, the circulation of blood through my body is achieved wholly regardless of my will). And finally, the initial object of the power which connects my will to my bodily movements is not the limb which I wish to move, but rather, different portions of the body which did not even register into consideration when I willed to move. The power itself whereby the will actualizes itself via the body thus remains completely unknown.
And the same problems accompany the even more simple act of thought. I desire to produce the mental image of a pyramid in the desert, and immediately the image is within my mind. Yet even here I remain completely unaware of the power whereby the mind produces the thought. Furthermore, why is it the case that I can control my thoughts more readily than my passions? Third, why is it the case that the will is not itself sufficient to realize an idea or mental state, but rather, the ability of the will to actualize itself depends upon attendant circumstances (e.g., a diabetic who wishes to concentrate on Hume’s arguments cannot do so if her blood sugar level is too low or too high—however much she wills to do so, she will find that her will is frustrated). And finally, by what strange mechanism is the mind able to produce an image as though ex-nihilo? My mind itself most certainly does not contain within itself the reality of an Egyptian pyramid, and yet it is able to produce an image of one. The effect is not composed of the cause.
From all of this, it follows that our only certainty—if the word be allowed—with regard to a cause and effect is experience. I have dropped a pen many times in the past, and in each case, the pen immediately fell downward. The experience of this phenomenon many times allows me to infer that the cause (dropping my pen) will be followed by the effect (the pen’s falling downward). Since it is the case that the power itself which connects the cause with the effect remains wholly obscure to me, I have no right to claim a priori that the pen will necessarily fall if I drop it; I can only be sure that this is what has always happened in the past, and I therefore expect that the same will be the case in the future.
Finally, Hume notes that God is commonly used as a means of bridging this explanatory gap. For example, the power whereby the pen falls to the ground would in this case either be identified with, or attributed to the will of, God. After disputing the notion that such a dependence of all things upon God would serve to ascribe fitting glory to the Almighty (for would it not be a more powerful proof of his omnipotence were he able to grant power, independent of himself, to creatures?), Hume goes on to show the inadequacy of the explanatory power of this hypothesis. For in the first place, this hypothesis has no ground whatever in experience, and second, it does no more than explain the obscure by virtue of the more obscure.
Thus we see that, according to David Hume, the notion of a necessary connection between a cause and its effect is dubious. The reason why he arrives at this conclusion is, it seems, due to his restricted epistemology. Just as a blind man would perhaps be unable to posit the form of a chair as the object of his aggregate sensations derived from touching one, so too Hume is unwilling to grant that two objects are actually connected if he fails to see the tie which binds them together. He refuses to affirm that which he has not directly experienced, and he is thus forced to admit of an agnosticism with regard to perhaps the commonest component of our experience.