David Hume: Are Cause and Effect Always Linked?

How does the philosopher David Hume’s skepticism about causation lead him to develop the concept of the necessary connection?

Jun 27, 2023By Luke Dunne, BA Philosophy & Theology
hume cause effect necessary connection


Why do we perceive there to be a fixed connection between causes and effects? Is it simply because there is an immutable, distinct connection? Not if we believe Hume, who was skeptical about this kind of further fact account of causation.


This skepticism raises, in turn, another question: if this is true, why do we struggle to accept that there is no “real” connection between these things? What, on a more skeptical account, is the connection between causes and effects? This article hopes to explore Hume’s answer to these questions. We will discuss Hume’s skepticism about causation, setting out the basis of this skepticism before pivoting to his characterization of the “necessary connection” between cause and effect. This article will then conclude with a critical discussion of the idea of “force” in Hume’s theory of mind.


Positive and Negative Aspects of David Hume’s Philosophy

allan ramsey hume oil painting
Portrait of David Hume by Allan Ramsay, 1766, via Google Arts and Culture.


To understand the role which the necessary connection plays in Hume’s philosophy, we have to understand the following distinction: the difference between the negative and positive elements of Hume’s thought. That is, between the aspects of his philosophy which are decidedly skeptical, and those elements which seek to explain why things are as they are, rather than explaining why they are not as they seem.


It is worth clarifying that these should not necessarily be seen as systematically related. Hume doesn’t begin with a clearly demarcated “negative phase” and then move on to his “positive phase.” Rather, these are the interpretative categories by which we can understand some of the elements of Hume’s thought that seem to pull against one another.


Get the latest articles delivered to your inbox

Sign up to our Free Weekly Newsletter

It is lastly worth noting that the skeptical elements of Hume’s work have driven interpretations of his philosophy for a very long time: they are the basis of his philosophical reputation, and yet this over-fixation on the negative aspect of Humean philosophy has led many to neglect great deal of what is most interesting about his thought.


David Hume on Causation

newtons cradle
Image of Newton’s cradle, via Pixabay.


Having said that, it is worth clarifying which negative elements of Hume’s philosophy underly the positive concept of necessary connection. One of the most important parts of Hume’s philosophy is his deflationary account of causation. Here is a famous quote from Hume’s Enquiry concerning Human Understanding:


“When I see, for instance, a billiard-ball moving in a straight line towards another; even suppose motion in the second ball should by accident be suggested to me, as the result of their contact or impulse; may I not conceive, that a hundred different events might as well follow from the cause? … All these suppositions are consistent and conceivable.”


It is tempting to take Hume for a fool, given that one ball striking another can, in fact, be plotted and measured in an extremely precise way. The results of one ball striking another (once all of the relevant variables are accounted for) is not liable to change from one instance to another. However, this response makes Hume’s point for him. He is categorically not suggesting that anything might actually happen to a billiard ball (when might is understood in a fairly practical way), but rather that in spite of the consistent relation between one ball striking another and the effect upon the ball it struck, this causal relationship has no strictly rational basis.


By this, Hume means only that we can always conceive of the ball being struck and instead floating into the air gradually, or remaining perfectly still, or any number of other things.


The Rational Foundation of Causation

diagram thought
Diagram of human thought, author unknown. Found in Utriusque Cosmi, Maioris scilicet et Minoris (1617-21). Via the Public Domain Review.


The point, as Hume has it, is this: “That there is nothing in any object, consider’d in itself, which can afford us a reason for drawing a conclusion beyond it; […] even after the observation of the frequent or constant conjunction of objects, we have no reason to draw any inference concerning any object beyond those of which we have had experience.”


Let’s leave aside whatever issues we might or might not have with Hume’s view of causation at this stage. It now remains for Hume to explain how our belief in the succession of events comes to be the way it is in light of the absence of a rational basis for this succession. Indeed, one way of understanding Hume’s work as a whole is an attempt to explain why we hold the beliefs we do in spite of the lack of a rational foundation for them (and, indeed, in spite of the general impotence of reason as such).


billiard painting
An Imperial Pietre Dure Plaque of The Billiard Players by Giuseppe Zocchi, ca. 1752-1755, via Christie’s.


There is, Hume claims, a “union in the imagination” between preceding event A and subsequent B when there is a constant conjunction between As and Bs. Given that it is not reasoning on which the transition is based, it must rather be that we simply find B follows in our minds where there is A. Hume thinks that this is automatic and unreflective:


“Nature, by an absolute and uncontroulable necessity has determin’d us to judge as well as to breathe and feel; nor can we any more forbear viewing certain objects in a stronger and fuller light, upon account of their customary connexion with a present impression, than we can hinder ourselves from thinking as long as we are awake, or seeing the surrounding bodies, when we turn our eyes towards them in broad sunshine.”


This is the crux of the necessary connection. Clearly, there are certain cases in which this picture seems accurate — when one is at the edge of the cliff, no reflection is required to know why one ought not to step over the edge.


The Experimental Method

experiment drawing
Image of the Tyndall experiment, via etc.usf.edu.


That said, it isn’t enough for Hume to say that an idea of B arises in a succession following A. As Barry Stroud writes, “When we get an impression of an A we do not just get an idea of a B—we actually come to believe that a B will occur. That is just the inference Hume wants to explain. All that has been explained so far is why the idea of a B comes into the mind.” Indeed, as Stroud stresses, “Hume’s further explanation of how an actual belief arises is primarily an explanation of how believing something differs from merely having an idea of it.”


How does Hume end up distinguishing holding a belief from merely having an idea? Hume’s philosophy has at its core a straightforward, self-conscious, and clearly stated project — the application of the experimental method of the natural sciences to human nature. Therefore, when faced with a problem, Hume often falls back on the method inscribed in the project as a whole. Here, he wants to treat the question of what constitutes a belief “as a question in natural philosophy, which we must determine by experience and observation.”


A Matter of Force: David Hume on Belief

allan ramsay hume painting
Portrait of David Hume by Allan Ramsay, 1754, via National Galleries Scotland.


Hume wishes to claim that what distinguishes a belief is a matter of force. “I wou’d willingly establish it as a general maxim in the science of human nature, that when any impression becomes present to us, it not only transports the mind to such ideas as are related to it, but likewise communicates to them a share of its force and vivacity.”


Yet Hume has stumbled here, especially with respect to his methodological commitment to observe how beliefs normally arise. We recognize that he has made an error in light of the following example he gives, purportedly in defense of this conception of a belief:


“If one person sits down to read a book as a romance, and another as a true history, they plainly receive the same ideas, and in the same order; nor does the incredulity of the one, and the belief of the other hinder them from putting the very same sense upon their author. His words produce the same ideas in both; tho’ his testimony has not the same influence on them. The latter has a more lively conception of all the incidents.”


brain activity
Image depicting brain activity, by the Glass Brain Project. Via WIRED UK.


It is this last sentence that demonstrates the weakness of Hume’s theory. We might be far more invested in our novel; indeed, we might find we have a far stronger conception of the characters in the novel than we do of historical figures in a dry history book.


All of this seems to be in service of defending another central element of Hume’s philosophy: his theory of mind. Hume wishes to claim that everything which goes on in our minds can be understood as an impression (a direct perception), an idea (the imprint of a perception or an aggregation thereof), or the associations between the various ideas. Yet, again following Stroud, the idea of a belief doesn’t seem to fit into any of these three categories. The “denigration of reason” has forced Hume to naturalize belief in a way that seems, at least, difficult to fathom.

Author Image

By Luke DunneBA Philosophy & TheologyLuke is a graduate of the University of Oxford's departments of Philosophy and Theology, his main interests include the history of philosophy, the metaphysics of mind, and social theory.