-- The Determinism and Freedom Philosophy Website, edited by Ted Honderich  --

Hume's is rightly the most celebrated thinking on causation in the history of all philosophy. The question it asks is what the connection really is between an effect and what precedes it. What is the fact to which we refer when we say that that the effect was made necessary by the cause or the causal circumstance? Hume's answer given below, which follows on a long inquiry into other ideas, is the simple one that all counterparts of the cause or causal circumstance are followed by counterparts of the effect. The connection between the cause and the effect is no more than that they were an instance of things constantly conjoined, a constant conjunction. At any rate, that is all that is true in the world -- putting aside our thinking and feeling about the connection. Is what Hume says true? That is another question. There is splendid philosophy that is not true. It does always give rise to truth.


But to hasten to a conclusion of this argument, which is already drawn out to too great a length: We have sought in vain for an idea of power or necessary connection, in all the sources from which we could suppose it to be derived. It appears, that, in single instances of the operation of bodies, we never can, by our utmost scrutiny, discover any thing but one event following another; without being able to comprehend any force or power, by which the cause operates, or any connection between it and its supposed effect 

The same difficulty occurs in contemplating the operations of mind on body; where we observe the motion of the latter to follow upon the volition of the former; but are not able to observe or conceive the tie, which binds together the motion and volition, or the energy by which the mind produces this effect. The authority of the will over its own faculties and ideas is not a whit more comprehensible: So that, upon the whole, there appears not, throughout all nature, any one instance of connection, which is conceivable by us. All events seem entirely loose and separate. One event follows another; but we never can observe any tie between them. They seem conjoined, but never connected. 

And as we can have no idea of any thing, which never appeared to our outward sense or inward sentiment, the necessary conclusion seems to be, that we have no idea of connection or power at all, and that these words are absolutely without any meaning, when employed either in philosophical reasonings, or common life.

But there still remains one method of avoiding this conclusion, and one source which we have not yet examined. When any natural object or event is presented, it is impossible for us, by any sagacity or penetration, to discover, or even conjecture, without experience, what event will result from it, or to carry our foresight beyond that object, which is immediately present to the memory and senses. Even after one instance or experiment, where we have observed a particular event to follow upon another, we are not entitled to form a general rule, or foretell what will happen in like cases; it being justly esteemed an unpardonable temerity to judge of the whole course of nature from one single experiment, however accurate or certain. 

But when one particular species of event has always, in all instances, been conjoined with another, we make no longer any scruple of foretelling one upon the appearance of the other, and of employing that reasoning, which can alone assure us of any matter of fact or existence. We then call the one object Cause; the other Effect. We suppose that there is some connection between them; some power in the one, by which it infallibly produces the other, and operates with the greatest certainty and strongest necessity.

It appears, then, that this idea of a necessary connection among events arises from a number of similar instances, which occur, of the constant conjunction of these events; nor can that idea ever be suggested by anyone of these instances, surveyed in all possible lights and positions. But there is nothing in a number of instances, different from every single instance, which is supposed to be exactly similar; except only, that after a repetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usual attendant, and to believe, that it will exist. This connection, therefore, which we feel in the mind, this customary transition of the imagination from one object to its usual attendant, is the sentiment or impression, from which we form the idea of power or necessary connection. 

Nothing farther is in the case. Contemplate the subject on all sides: you will never find any other origin of that idea. This is the sole difference between one instance, from which we can never receive the idea. of connection, and a number of similar instances, by which it is suggested. The first time a man saw the communication of motion by impulse, as by the shock of two billiard-balls, he could not pronounce that the one event was connected: but only that it was conjoined with the other. After he had observed several instances of this nature, be then pronounces them to be connected. What alteration has happened to give rise to this new idea of connection? Nothing but that he now feels these events to be connected in his imagination, and can readily foretell the existence of one from the appearance of the other. 

When we say, therefore, that one object is connected with another, we mean only, that they have acquired a connection in our thought, and give rise to this inference, by which they become proofs of each other’s existence: A conclusion, which is somewhat extraordinary; but which seems founded on sufficient evidence. Nor will its evidence be weakened by any general diffidence of the understanding, or sceptical suspicion concerning every conclusion, which is new and extraordinary. No conclusions can be more agreeable to scepticism than such as make discoveries concerning the weakness and narrow limits of human reason and capacity.

And what stronger instance can be produced of the surprising ignorance and weakness of the understanding, than the present? For surely, if there be any relation among objects, which it imports to us to know perfectly, it is that of cause and effect. On this are founded all our reasonings concerning matter of fact or existence. By means of it alone we attain any assurance concerning objects, which are removed from the present testimony of our memory and senses. The only immediate utility of all sciences, is to teach us, how to control and regulate future events by their causes. Our thoughts and enquiries are, therefore, every moment, employed about this relation: Yet so imperfect are the ideas which we form concerning it, that it is impossible to give any just definition of cause, except what is drawn from something extraneous and foreign to it. Similar objects are always conjoined with similar. Of this we have experience. 

Suitably to this experience, therefore, we may define a cause to be an object, followed by another, and where all the objects, similar to the first, are followed by objects similar to the second. Or, in other words, where, if the first object had not been, the second never had existed. The appearance of a cause always conveys the mind, by a customary transition, to the idea of the effect. Of this also we have experience. We may, therefore, suitably to this experience, form another definition of cause; and call it, an object followed by another, and whose appearance always conveys the thought to that other.

But though both these definitions be drawn from circumstances foreign to the cause, we cannot remedy tthis inconvenience, or attain any more perfect definition, which may point out that circumstance in the cause, which gives it a connection with its effect. We have no idea of this connection; nor even any distinct notion what it is we desire to know, when we endeavour at a conception of it. We say, for instance, that the vibration of this string is the cause of this particular sound, But what do we mean by that affirmation? We either mean, that this vibration is followed by this sound, and that all similar vibrations have been followed by similar sounds: Or, that this vibration is followed by this sound, and that upon the appearance of one, the mind anticipates the senses, and forms immediately an idea of the other. We may consider the relation of cause and effect in either of these two lights; but beyond these, we have no idea of it.

To recapitulate, therefore, the reasonings of this section: Every idea is copied from some preceding impression or sentiment; and where we cannot find any impression, we may be certain that there is no idea. In all single instances of the operation of bodies or minds, there is nothing that produces any impression, nor consequently can suggest any idea, of power or necessary connection. But when many uniform instances appear, and the same object is always followed by the same event; we then begin to entertain the notion of cause and connection. We then feel a new sentiment or impression, to wit, a customary connection in the thought or imagination between one object and its usual attendant; and this sentiment is the original of that idea which we seek for. For as this idea arises from a number of similar instances, and not from any single instance; it must arise from that circumstance, in which the number of instances differ from every individual instance. But this customary connection or transition of the imagination is the only circumstance, in which they differ. In every other particular they are alike. The first instance which we saw of motion, communicated by the shock of two billiard-bails (to return to this obvious illustration) is exactly similar to any instance that may, at present, occur to us; except only, that we could not, at first, infer one event from the other; which we are enabled to do at present, after so long a course of uniform experience. 

I know not, whether the reader will readily apprehend this reasoning. I am afraid, that, should I multiply words about it, or throw it into a greater variety of lights, it would only become more obscure and intricate. In all abstract reasonings, there is one point of view, which, if we can happily hit, we shall go farther towards illustrating the subject, than by all the eloquence and copious expression in the world. This point of view we should endeavour to reach, and reserve the flowers of rhetoric for subjects which are more adapted to them.

Editor's Postscript
For the editor's disagreement with Hume's account, a disagreement shared with many other philosophers, go to Causality or Causation -- the Fundamental Fact Plainly Explained. This comes from Ted Honderich, A Theory of Determinism: The Mind, Neuroscience and Life-Hopes (Oxford University Press), pp. 13-70, which also appears in Mind and Brain (OUP), pp. 13-70. For a brisk summary of the same view, see How Free Are You: The Determinism Problem (OUP), 1st edition, Ch. 1, 2nd edition, Ch. 2. 

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