Hume’s Theory of Causal Relations

by :
Mark Lindner

In An Enquiry Concerning Human Understanding, David Hume addresses the fundamental question, “What are the limits of our understanding?” He reasons his way to the conclusion that all matters of fact are founded on the relation of Cause and Effect. The Oxford Dictionary of Philosophy defines causation as “one of the central problem areas of metaphysics. Causation is the relation between two events that holds when, given that one occurs, it produces, or brings forth, or determines, or necessitates the second; equally we say that once the first has happened the second must happen or that the second follows from the first.”1 Just what is this relation of cause and effect? My purpose in this essay is to explain Hume’s theory of causal relations. I will briefly lay out his argument up till the conclusion in Sect. IV Part I that all matters of fact are founded on the relation of cause and effect and then will explicate his theory from there. For the purpose of this essay I will assume that the arguments leading up to the causal relation theory are valid, sound and correct. It is my intention to accept Hume’s theory of causal relations.
In Section II of the Enquiry Hume claims that all perceptions of the mind can be divided into two classes, “which are distinguished by their different degrees of force and vivacity. The less forcible and lively are commonly denominated THOUGHTS or IDEAS.”2 The more lively perceptions are called IMPRESSIONS. Thoughts are what we are conscious of when we reflect on the more lively impressions and “the most lively thought is still inferior to the dullest sensation.”3 Hume provides us with two arguments to show that this is so. His first shows that when we analyze any thought, however simple or complex, we will find that it can be reduced to simple ideas that arose from, or “were copied from a precedent feeling or sentiment.”4 His second claims that someone without a specific functioning sense organ would not have the corresponding ideas. Thus, a blind man can have no notion of colors, or a deaf man of sounds; no impressions, no subsequent corresponding ideas. Hume claims to have shown that contra Descartes, there are no ‘clear and distinct’ ideas. He says that “all ideas, especially abstract ideas, are naturally faint and obscure.”5 In Sect. III, he states that there seems to be some sort of universal principle, which binds together or associates simple ideas into compound ones. He claims that there are three principles of connection among ideas. These are “namely, Resemblance, Contiguity in time or place, and Cause or Effect.”6 In Sect. IV Part I, Hume divides the objects of human reason into two kinds, Relations of Ideas, and Matters of Fact. Relations of ideas are those which are intuitively or demonstratively certain, such as geometry, algebra and arithmetic. Matters of fact are different, in that the contrary of every matter of fact is possible. The mind is able to conceive of a matter of fact and its opposite equally well with no contradiction. Thus, Hume asks, “what is the nature of that evidence, which assures us of any real existence and matter of fact, beyond the present testimony of our senses, or the records of our memory?”7 Hume postulates that all reasoning about matters of fact is founded on the relation of cause and effect. So, again, just what is this relation of cause and effect?
Ask a man why he believes any matter of fact, and his reply will be another fact. A connection of some sort is constantly supposed between the first fact and the one that is inferred from it. How do we arrive at the knowledge of cause and effect? Hume proposes a general proposition that without exception, knowledge of the cause and effect relation is not discernable by a priori reasoning, contra Leibniz, Spinoza and Descartes; but that it arises from our experience of particular objects or events that are ‘constantly conjoined.’ “Two events A and B are constantly conjoined if whenever one occurs the other does.”8
Let’s do a thought experiment. Ask someone to imagine that they are brought all of a sudden into this world. They would believe themselves capable of inferring the effect of some cause, such as that one billiard ball would confer motion upon another; such is the strength of custom or habit of mind. Present someone with some object or event that they’ve never before experienced and ask them to tell you what the effect would be. They must imagine or invent some event to serve as the effect; “and it is plain that this invention must be entirely arbitrary.”9 “The effect is totally different from the cause, and consequently can never be discovered in it.”10 Thus, the supposed connection that we infer between the cause and the effect is similarly arbitrary. Since every effect is a separate event from its cause and can not be found in the cause, every a priori conception of the effect must be entirely arbitrary. Without the aid of observation and experience we strive in vain to infer any cause or effect. As to what the causes of our general causes or scientific laws are, Hume says that “these ultimate springs and principles are totally shut up from human curiosity and enquiry.”11
Have we gotten anywhere besides generating more questions? When we asked, “What is the nature of our reasoning concerning matters of fact?” we answered that they are founded on the cause and effect relation. When we asked, “What is the nature of our reasoning about that relation?” we replied, experience. Now we must ask “What is the basis of our conclusions from experience?” Hume claims that “even after we have experience of the operations of cause and effect, our conclusions from that experience are not founded on reasoning, or any process of the understanding.”12
It must be admitted that nature has kept her secrets from us. We have been allowed the knowledge of a few superficial qualities of objects, but the powers and principles, which underlie the laws of nature, are kept from us. Even though we are ignorant of these powers, whenever we encounter like sensible qualities we always presume like secret powers, that is, we expect like effects. What power of thought gives us this presumption? Certainly, past experience gives us direct and certain information about objects or events at that specific time at which we were observing them. But why do we extend this experience to future times and similarly appearing circumstances? We have two propositions here which are not the same. “I have found that such an object has always been attended with such an effect, and I foresee, that other objects, which are, in appearance, similar, will be attended with similar effects.”13 Hume insists that the second proposition is always inferred from the first. But by what chain of reasoning is this inference made? It is certainly not intuitive. It is not a contradiction that the course of nature as we have experienced it so far might change. An object, like one that we have preciously encountered, may have different effects than what we would normally infer based on previous experience. This claim is certainly intelligible. Hume claims that “whatever is intelligible, and can be distinctly conceived, implies no contradiction, and can never be proved false by any demonstrative argument or abstract reasoning a priori.”14 So far, we have argued that (1) all reasoning concerning existence is founded on the cause and effect relationship; (2) all of our knowledge concerning that relationship is founded on experience; and that (3) all our experiential conclusions are based on the supposition that the future will conform to the past. Now, when we try to prove this supposition by probable arguments, or by arguments regarding existence, we find ourselves in a vicious circle. Hume concludes that “from causes, which appear similar, we expect similar effects. This is the sum of all our experimental conclusions.”15
But, as long as there is any suspicion that nature may change, the past can be no rule for the future, and thus, experience becomes useless. It can give rise to no inference. The ignorant, and even infants, can learn the effects of causes through experience. But if you say it is through some process of reason, please tell us what it is. Do not hesitate or say that it is abstruse, since clearly it must be accessible to a mere infant. Clearly then, it is not reasoning that allows us to suppose the future will resemble the past, or that similarly appearing causes will have similar effects.
Let us try another thought experiment. Imagine that a person with a full faculty of reason and reflection, but no experience, were to be brought suddenly into the world. She would certainly observe a continual sequence of objects, and events following one from another, but she would not be able, at first, to reach the idea of cause and effect through any process of reason. The conjunction of seeming causes and effects might be arbitrary and casual with no reason to infer the existence of the effect from the appearance of the cause. Imagine now that she has acquired more experience, living a long and attentive life, observing many similar events and objects to be constantly conjoined. What is the consequence of all this experience? She immediately infers the existence of one object from the experience of the other. But, through all her experience, she has acquired no idea of the secret power by which one entails the other. There must be some principle by which she forms these cause and effect conclusions.
Hume’s answer is that this principle is just a custom or habit of mind. When two objects are constantly conjoined, we come by habit alone to expect one from the appearance of the other. This explains why it is that we can draw an inference from a thousand occurrences that we are unable to draw from only one, when there is nothing in the thousand that is not in the one. “All inferences from experience, therefore, are effects of custom, not of reasoning.”16 This view is a type of projectivism. “Projectivism denotes any view which sees us as similarly projecting upon the world what are in fact modifications of our own minds.”17 For Hume, the causal order of events is a projection of our own mental habits in the way they follow from one another.
In Section VII of the Enquiry, entitled “Of the Idea of Necessary Connexion,” Hume is no longer interested in our knowledge of casual relationships. Here he is concerned with an analytical or definitional account of causality. Apart from how we know whether causal relationships exist in the world, what is causality? “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 connexion between it and its supposed effect.” “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.” “We then call the one object, Cause; the other, Effect. We suppose, that there is some connexion between them; some power in the one, by which it infallibly produces the other, and operates with the greatest certainty and strongest necessity.”18
Hume brings us back to the difference between one instance and a repetition of instances. He claims that the only difference is that after a repetition of instances the mind is carried by habit to expect the usual connecting attendant cause or effect. We feel this transition of the imagination in our minds. It is from this transition that we form the idea of a necessary connection. How did we get connection from constant conjunction? By no means than other that we now feel these events to be connected in the imagination.
Hume is now ready to define causation. In fact, he gives us two definitions which has led to controversy as to how he should be interpreted. The first definition goes as follows:
“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 objects similar to the first are followed by objects similar to the second.”19
The second definition goes this way:
“The appearance of a cause always conveys the mind, by a customary transition, to the idea of the effect. Of this we also 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.”20
Hume illustrates both definitions with the same example of the vibration of this string is the cause of this particular sound. We mean either, that this vibration is followed by this sound and similar vibrations have been followed by similar sounds; or, that this vibration is followed by this sound, and that when the one appears, the mind anticipates the senses and forms 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.”21
These definitions are to some extent loose and ambiguous. Hume shifts back and forth between speaking of causes and effects as ‘objects’ and as ‘events.’ In both definitions he speaks of them as ‘objects.’ But leading up to the definitions he uses ‘event(s)’ repeatedly.
“It is more accurate to regard causes and effects as events than as objects. We can speak of the objects themselves as causes only in a derivative sense, based on the consideration that events are generally changes in objects. For example, we can say that one billiard ball – a certain object – is “the cause” of motion in another, insofar as it is that ball which, by hitting the other, causes the motion. It is obvious, nevertheless, that the cause is not just the ball as such, but its collision with the other ball, which is itself an event. It is even more obvious that the effect is not the other ball itself, but rather that ball’s movement following from the collision, which is also an event.”22
I maintain that Hume’s own position was that causes and effects are events rather than objects. If one looks carefully at the Enquiry and A Treatise of Human Nature, one finds that ‘event’ talk clearly outnumbers ‘object’ talk. Even if he was looser than he should have been and used ‘object’ in the definitions, I believe that he would maintain that ‘event’ talk is proper to the cause and effect relation.
In this essay I have tried to elucidate Hume’s theory of causal relations. His conclusion is that we have a custom or habit of mind that lets us infer a cause and effect relationship. I have laid out his argument showing that all matters of fact are founded on the relation of cause and effect. I then explicated his theory by showing that all reasoning concerning existence is founded on the cause and effect relationship; all of our knowledge concerning that relationship is founded on experience; and that all our experiential conclusions are based on the supposition that the future will conform to the past. So it is only from a custom or habit of mind that this supposition arises.
I fully agree with Hume on this matter of causal relations. There may actually be, that is ontologically exist, cause and effect relations. But, we as finite creatures, shielded from nature, supposing there to be some secret power by which an effect follows from a cause, can never know if this is the case, or assuming that it is, which cause and effect relationships actually do exist.
Bibliography
Hume, David, An Enquiry Concerning Human Understanding in Cahn, Steven M., ed. Classics of Western Philosophy, Fourth Edition. Indianapolis: Hackett Publishing Company, 1995.
Blackburn, Simon, The Oxford Dictionary of Philosophy, New York: Oxford University Press, 1996.
Dicker, George, Hume’s Epistemology and Metaphysics: An Introduction, New York: Routledge, 1998.
1 The Oxford Dictionary of Philosophy, p. 59.
2 Hume, David, An Enquiry Concerning Human Understanding, p. 838.
3 ibid., p. 838.
4 ibid., p. 839.
5 ibid., p. 840.
6 ibid., p. 841.
7 ibid., p. 842.
8 The Oxford Dictionary of Philosophy, p. 78.
9 Hume, David, An Enquiry Concerning Human Understanding, p. 844.
10 ibid., p. 844.
11 ibid., p. 845.
12 ibid., p. 846.
13 ibid., p. 847.
14 ibid., p. 847.
15 ibid., p. 849.
16 ibid., p. 852.
17 The Oxford Dictionary of Philosophy, p. 305.
18 Hume, David, An Enquiry Concerning Human Understanding, p. 867-868.
19 ibid., p. 869.
20 ibid., p. 869.
21 ibid., p. 869.
22 Dicker, George, Hume’s Epistemology and Metaphysics: An Introduction, p. 112.