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Hume on Causation, Relations and “Necessary Connexions”



Hume on Causation, Relations and “Necessary Connexions”

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Jason Zarri

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1. Introduction

A specter is haunting Hume scholarship: the specter of the “New Hume.” Contrary to more traditional interpretations, according to which Hume rejects belief in any conception of causation that invokes (metaphysically) necessary connections between distinct existences, proponents of the New Hume hold that Hume at the least allowed for the possibility of such connections—it’s just that he thought we couldn’t know much, if anything, about them, if we assume that they do exist.

I will argue that the views of the “New Humers” (as I shall call them) are mistaken. I will begin by discussing their reading of Hume on causation, using Galen Strawson as a foil. I then examine the relation between Hume’s view of relations (pun intended) and his account of “necessary connexions”. Next, I argue that this account, once properly understood, shows that he did not believe in what we would think of as necessary connections while at the same time explaining why, as the New Humers point out, Hume sometimes writes in ways that can make it sound like he does, as well as reconciling Hume’s two definitions of causation. After that, I answer objections, and then raise some doubts about Hume’s account before finally concluding the paper.

2. A Tale of Two Humes

On more-or-less traditional ways of reading Hume, he was either a reductionist or an eliminitivist about causation and/or “necessary connexions.” Causation either does not involve a genuinely necessary connection, and is reducible to something like a regular association between types of events, or else does involve a genuinely necessary connection, and is to be eliminated in favor of a regular association between types of events.

In this section I will address some apparent textual evidence adduced by Galen Strawson, a prominent New Humer, to show that Hume, contrary to the more traditional interpretations, did believe in what Simon Blackburn has called1 “thick connections”. Strawson expresses his own belief in such connections as follows:

For present purposes, then, ‘Causation’ may be merely negatively defined: it covers any essentially non-regularity-theory conception of causation. More positively (if essentially unspecifically): to believe that causation is in fact Causation is simply to believe (A) that there is something about the fundamental nature of the of the world in virtue of which the world is regular in its behaviour, and (B) that that something is what causation is, or rather is at least an essential part of what causation is or involves.” (The Secret Connexion pp. 84-5; footnote omitted)

I think Hume—the good-old-fashioned Hume that most philosophers have known and quite a few of whom have loved—would object to this on the grounds that we have no firmer grip on the notion of the world’s behaving in a certain way “in virtue of” its “fundamental nature” than we have on Causation, thick connections, secret powers, and the like.But, in any case, what evidence does Strawson have for taking Hume to be a realist about thick connections, “capital-‘C’ Causation” and similar things? One of his examples is this passage (Cited on p. 154 of his The Secret Connexion):

I answer this objection, by pleading guilty, and by confessing that my intention never was to penetrate into the nature of bodies, or explain the secret causes of their operations. For besides that this belongs not to my present purpose, I am afraid, that such an enterprise is beyond the reach of human understanding, and that we can never pretend to know body otherwise than by those external properties, which discover themselves to the senses. As to those who attempt any thing farther, I cannot approve of their ambition, till I see, in some one instance at least, that they have met with success. (Treatise, my emphases)


This might seem to show that Hume believed in secret powers, but it is less convincing than it may at first appear. Strawson neglects to give the section number of this passage, and also fails to cite the objection that Hume takes himself to be replying to, which I reproduce here:

It will probably be said, that my reasoning makes nothing to the matter in hands and that I explain only the manner in which objects affect the senses, without endeavouring to account for their real nature and operations. Though there be nothing visible or tangible interposed betwixt two bodies, yet we find BY EXPERIENCE, that the bodies may be placed in the same manner, with regard to the eye, and require the same motion of the hand in passing from one to the other, as if divided by something visible and tangible. This invisible and intangible distance is also found by experience to contain a capacity of receiving body, or of becoming visible and tangible. Here is the whole of my system; and in no part of it have I endeavour’d to explain the cause, which separates bodies after this manner, and gives them a capacity of receiving others betwixt them, without any impulse or penetration. (Treatise

In this context, it is far more likely that Hume’s talk of secret powers is about unobserved, but perhaps in principle observable qualities or relations of objects that explaintheir susceptibility to standing in certain spatial relations, than that it is about secret causal powers. I believe that similar passages may all be accounted for: They are, if not similarly taken out of context, either cases of irony, speaking (technically, writing) loosely, or most importantly, cases of us—that is, contemporary philosophers—having a different conception of necessity and of the ontological status of relations from Hume. I will try to explain what these differences are, and why they are important, in the sections 3 and 4.

3. Hume, Relations and “Necessary Connexions”

One factor that seems to have been neglected in discussions of Hume on causation and necessary connection is Hume’s opinion on the ontological status of relations. Here, in very brief terms, is Hume’s view:

The word RELATION is commonly used in two senses considerably different from each other. Either for that quality, by which two ideas are connected together in the imagination, and the one naturally introduces the other, after the manner above-explained: or for that particular circumstance, in which, even upon the arbitrary union of two ideas in the fancy, we may think proper to compare them.—(Treatise 1.5.1, my emphases)

Now, if (to put it in contemporary terminology) relations are grounded in or constituted by a connection or union of ideas in the imagination (or “fancy”), they depend for their existence on certain mental operations—although their “foundations”, which lie in the monadic properties of the things they relate, could endure even if all creatures endowed with minds were to go extinct,2 these being the “qualit[ies]” that produce the connection in the imagination. However, though relations are grounded in certain properties of or facts about objects, it would on this view be a mistake to reify relations and conclude that they themselves, which consist in ideas and mental operations, could exist independently of a mind.

It is important to remember that due to the influence of Aristotle and the medieval Scholastics, in early modern philosophy relations were often viewed as being “constructible” from the properties or accidents of the their relata. This view may be roughly characterized in the following terms, in a few passages from an article by JeffreyBrower on medieval views on relations in The Stanford Encyclopedia of Philosophy:

The rejection of polyadic [i.e. multi-place, relational] properties might seem to commit one to a form of anti-realism about relations—that is, to the view that relations exist only in the mind. This was, in fact, the position of Peter Auriol. (“Medieval Theories of Relations,” section 3.2, http://plato.stanford.edu/archives/win2010/entries/relations-medieval/.)

According to Albert [The Great], the problem with arguments of the sort Auriol gives is that they rely on a questionable assumption, namely: if there are no real polyadic forms or properties, then there is nothing in extramental reality to correspond to our relational concepts. This assumption would be true, he suggests, if our conceptual framework displayed an exact isomorphism to the structure of the world. But it does not, and hence there is no reason in principle why a polyadic concept cannot have something non-polyadic corresponding to it. […]For most medieval philosophers, then, the question is not whether there are any things in extramental reality corresponding to our relational concepts, but what these things are like in themselves. (“Medieval Theories of Relations,” section 3.3, http://plato.stanford.edu/archives/win2010/entries/relations-medieval/, footnotes omitted)

It should not be surprising, then, that the relation of necessary connection “belongs only to the mind”:

But when, instead of meaning these unknown qualities, we make the terms of power and efficacy signify something, of which we have a clear idea, and which is incompatible with those objects, to which we apply it, obscurity and error begin then to take place, and we are led astray by a false philosophy. This is the case, when we transfer the determination of the thought to external objects, and suppose any real intelligible connexion betwixt them; that being a quality, which can only belong to the mind that considers them. (Treatise, my emphases)

While he regards all relations as mental, I think that for Hume the crux of the matter is the question of how, if at all, the relation of causation or of necessary connection is grounded in properties of or facts about the objects which we call ‘causes’ and ‘effects’. Hume tried to show that it is not founded on any of their monadic properties, nor is it reducible to any relations that are so founded.3 If we were acquainted with any such properties, they would give rise to such ideas as “power” and “force”—ideas which, Hume argues, we do not really have—and they would enable us to deduce what would follow on the appearance of an object merely by observing it,something which Hume argues we cannot do.

What is it about the causal relation that makes it count, not merely as a connection, but as a necessary connection? For Hume the answer is that there an important similarity between it and what most philosophers would regard as paradigms of necessity, such as the statement that two times two equals four and the statement that the sum of the angles of any (Euclidean) triangle is equal to the sum of two right angles. In both kinds of case the mind is determined to pass from one idea to another, and according to Hume this determination is what necessity is:

The necessary connexion betwixt causes and effects is the foundation of our inference from one to the other. The foundation of our inference is the transition arising from the accustomed union. These are, therefore, the same. (Treatise, my emphasis)

Thus as the necessity, which makes two times two equal to four, or three angles of a triangle equal to two right ones, lies only in the act of the understanding, by which we consider and compare these ideas; in like manner the necessity or power, which unites causes and effects, lies in the determination of the mind to pass from the one to the other. The efficacy or energy of causes is neither placed in the causes themselves, nor in the deity, nor in the concurrence of these two principles; but belongs entirely to the soul, which considers the union of two or more objects in all past instances. It is here that the real power of causes is placed along with their connexion and necessity. (Treatise, My emphases)


Yet there is at least one significant difference: In the paradigm cases of necessity the mind cannot help but pronounce that a certain relationship holds whenever is compares the ideas involved, but in the case of one event’s causing another Hume thinks we can easily conceive the one event to occur without the other. In both cases there is necessity, and in both cases there is a relation between ideas, but it is only in the former case that we have a relation of ideas, in the sense in which Hume uses that term.

4. Will the Real David Hume Please Stand Up?

What impact might this have on the “Old Hume” vs. “New Hume” debate? Did Hume believe in, or at least allow for the possibility of, capital-‘C’-Causation, “thick” connections, secret powers, and so on? He certainly allows for the existence of unknown qualities of objects—as well he should, otherwise the fact that someone cannot imagine the flavor of a pineapple, if they haven’t tasted one, would prove that the notion of an untasted flavor is incoherent—which of course it isn’t. Hume says,

I am, indeed, ready to allow, that there may be several qualities both in material and immaterial objects, with which we are utterly unacquainted; and if we please to call these POWER or EFFICACY, it will be of little consequence to the world. (Treatise )

The question is: Could any of these unknown qualities, whatever they may be, count as Causation, thick connections, secret powers, etc.? I’m inclined to agree with Peter Millican that, according to Hume, they wouldn’t.4 The only notion of necessity that we have is that of a feeling of determination or expectation (or the mental transition which they accompany). The feelings are either impressions—which represent nothing—or ideas, which only represent those impressions—and in neither case are they founded on anything in the external world except the precedence, contiguity, and constant conjunction of certain objects. Besides custom, the only possible source of an idea of a thick connection between external objects would be the fact that we could not have an idea of the one without having an idea of the other, that we could not so much as imagine or conceive of the one without imagining or conceiving of the other. But as long as our ideas of a cause and its effect are distinct, it is true that, as Hume says later in the Treatise, “…since all our perceptions are different from each other, and from every thing else in the universe, they are also distinct and separable, and may be considered as separately existent, and may exist separately…” (Treatise, and from the idea of the one we can never validly deduce that its usual effect (or anything else) will follow from it. If Hume’s “separability principle” is right, we could never deduce a priori what will follow upon what, no matter what ideas we may be acquainted with.

Furthermore, I believe that my interpretation of Hume’s views on relations and necessary connections can explain the apparent support that New Humers find for their views in Hume’s writings. Hume sometimes writes as though he believes in necessary connections, or secret powers, and sometimes he writes as though he doesn’t. I think this is because for him necessary connections are real, insofar as their grounds are, and as in the case of spatial relations mentioned in Section 2, these grounds, though knowable in principle, may currently be hidden from us—hence the talk of ‘secrecy’—although they are such that they would engender a belief in a necessary connection if we were aware of them. However, insofar as the grounds of relations of necessary connection are mental phenomena, they are not real independently of a real observing mind, and hence they are not real in quite the way that we would ordinarily take them to be. Thus sometimes Hume is emphasizing one aspect of his position, and sometimes another, and it is this that accounts for many of the cases where Hume seems to allow for the possibility of what we would regard as necessary connections.

I believe my interpretation can also reconcile an apparent tension between Hume’s two definitions of causation:

We may define a CAUSE to be “An object precedent and contiguous to another, and where all the objects resembling the former are placed in like relations of precedency and contiguity to those objects that resemble the latter.” If this definition be esteem’d defective, because drawn from objects foreign to the cause, we may substitute this other definition in its place, viz. “A CAUSE is an object precedent and contiguous to another, and so united with it, that the idea, of the one determines the mind to form the idea of the other, and the impression of the one to form a more lively idea of the other.” (Treatise

One thing that has been said about these definitions is that they are not even extensionally equivalent. Simply consider a remote corner of the universe where there are as many regularities in the occurrence of events as you please, but no sentient beings around to observe them and hence to form the right kind of habitual associations to acquire a felt determination to infer one such occurrence from another. In that case the first definition is satisfied, while the second is not.

For my part, I think that once we distinguish a relation or relational concept from its grounds, we will recognize that the grounds can exist in circumstances where no observers are present to form the corresponding relational concept, and thus that a relation—causation, for instance—can in a sense still be said to exist in so far as observers would form that corresponding concept if they were present. In the first, objective definition, Hume has the grounds of causal relations in mind. In the second, subjective definition, he is considering the relations themselves as mental phenomena. We can consider any relation from two different perspectives: From one, we focus on the worldly items that our relational concepts apply to, or which they would apply to, were we around to observe them. From the other, we focus on the relational concept itself. Hume’s two definitions of causation are attempts to capture these two perspectives; and when understood as such, I think no real tension can be detected between them.

5. Objections Answered

One could object to my account on the grounds that I say that Hume believes in necessary connections even though he thinks the negations of propositions which assert such connections are conceivable, and hence possible. So on my interpretation Hume thinks that something could be necessary even though it could be otherwise, which seems absurd. How can something be necessary when its negation fails to be impossible?

My response is that the imagined objector is exactly right: The conclusion that something could be necessary even though it could be otherwise seems absurd. But it’s not absurd; at least, not for Hume. We must remember that on my interpretation of Hume, he simply doesn’t mean what we mean by ‘necessary’. Though it may sound strange to us to say that something which is necessary could have turned out not to be the case, for Hume necessity is simply a determination of the mind to pass from one idea to another. In some cases—relations of ideas—the negation of the connection is not possible, and in others—cases of causation—it is. On this account there is nothing strange about some proposition, which is actually necessary, possibly not being the case, no matter how strange it sounds to us.

One could also argue that the following passage is problematic for my interpretation of Hume’s view of relations:

As to what may be said, that the operations of nature are independent of our thought and reasoning, I allow it; and accordingly have observed, that objects bear to each other the relations of contiguity and succession: that like objects may be observed in several instances to have like relations; and that all this is independent of, and antecedent to the operations of the understanding. But if we go any farther, and ascribe a power or necessary connexion to these objects; this is what we can never observe in them, but must draw the idea of it from what we feel internally in contemplating them. (Treatise


But I think that what Hume means here is that it is the properties of objects or the facts about them that ground such relations which exist outside the mind, and which could exist without its activity. When it comes to causation, by contrast, the idea—and hence the relation—of “necessary connexion” is grounded in a feeling of determination or expectation which arises from the frequent observation of similar objects constantly being followed by other, similar objects. Because this inference and its attendant feeling are both mental phenomena, the idea of a necessary connection, unlike many other ideas of relations, cannot be supposed to hold of external objects independently of any mind.

6. Skepticism with Regard to Hume’s Account

Before closing I shall, in a Humean spirit, briefly raise some skeptical doubts about Hume’s own views.

Consider your favorite music album. You’ve listened to it a hundred times, and you know its songs by heart. Moreover, you know the ordering of the songs by heart. On hearing the end of one song, I’d wager, you form the idea of the next one, and believe that it will soon begin. Every time you listen to the album you hear those songs together—they are constantly conjoined in your experience. They are also temporally contiguous, and the one song always occurs prior to the other. Together, these factors are what give rise to your belief.

We have here everything which Hume regards as sufficient for belief in causation or necessary connection, and yet we plainly do not think that the events of the one song’s ending and the other one’s beginning are causally related. Granted, the songs might not really be constantly conjoined; they may be played separately in live performances, on the radio, or on your iPod; but we may suppose that they always occur together within a given person’s experience, for all we are enquiring about is their belief (or lack thereof) in a causal connection. Given that, this hypothetical person’s failure to form the belief that the ending of the one song causes the beginning of the other is an anomaly for Hume’s account of how we form causal beliefs. As neither the inference from the event of the one song’s ending to the other’s beginning nor the feeling of expectation to which it gives rise is enough to engender an ascription of causation or necessary connection, and as those ideas cannot arise from the other candidate sources that Hume considers, I think we would be justified in concluding that at least some ascriptions of causation or necessary connection cannot be accounted for on his principles.

This example also reveals, I think, that we have an idea of causation or necessary connection which goes beyond the sort that Hume believes in, and thus that when we make such causal claims we do “understand our own meaning”, and do not “ignorantly confound ideas” (Treatise we do so. I don’t have the space to mount a full argument here, nor to give a positive characterization of that conception. But in spite of that, I think my example shows that, since Hume’s criteria are not sufficient for the ascription of causation or necessary connection, when we do make such ascriptions we are ascribing something more than what Hume claims we are. There may or may not be something more to causation in reality, but that is of course a different question.

7. Conclusion of this Paper

In this paper I have tried to show the New Humers to be mistaken. I’ve argued that Hume’s view of relations makes him what could be described as a quasi-realist about causal relations, and indeed about all relations. However, though Hume did in a sense believe in causation and even in “necessary connexions,” he did not mean what we mean by ‘necessary’. For I have also tried to show that Hume held a mentalistic view of necessity, taking it to be a transition between ideas or the feeling of determination that accompanies such a transition. Admittedly, this has the consequence that for Hume some things which are necessary could still be otherwise. That doesn’t sound too pleasing to the ears of contemporary philosophers, but I believe the text of Hume’s Treatise makesit clear that that was what he thought. As Hume himself said later on in his Enquiry concerning Human Understanding, “A wise man…proportions his belief to the evidence” (Section 10.4).





Blackburn, Simon. Hume and Thick Connexions.Philosophy and Phenomenological Research, Vol. 50, Supplement (Autumn, 1990), pp. 237-250

Brower, Jeffrey, “Medieval Theories of Relations”, The Stanford Encyclopedia of Philosophy (Winter 2010 Edition), Edward N. Zalta (ed.), URL = <http://plato.stanford.edu/archives/win2010/entries/relations-medieval/>.

Hume, David. An Enquiry concerning Human Understanding, Edited by Tom L. Beauchamp. Oxford University Press, Oxford 1999.

Hume, David. A Treatise of Human Nature, Edited by David Fate Norton and Mary J. Norton. Oxford University Press, Oxford 2001.

Millican, Peter. “Humes Old and New: Four Fashionable Falsehoods, and One Unfashionable Truth,” Proceedings of the Aristotelian Society, Supplementary Volumes, Vol. 81 (2007), pp.163-199

Strawson, Galen. The Secret Connexion: Causation, Realism, and David Hume. Oxford University Press, Oxford 1989.



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1Hume and Thick Connexions.Philosophy and Phenomenological Research, Vol. 50


2In the case of causation, the foundation lies in the temporal precedence and spatial contiguity of certain pairs of objects, together with the constant conjunction of all relevantly similar pairs of objects.


3Temporal priority and spatial contiguity are not founded on any monadic properties of their relata; as Hume says, they can be changed without any change in the ideas. Still, despite his mentalism, he could posit that such relations exist because they are grounded in primitive facts which concern both of the related objects. I don’t believe that Hume could think that the same could be true of causation, for reasons similar to those given in section 4 below.


4See his “Humes Old and New: Four Fashionable Falsehoods, and One Unfashionable Truth,” Proceedings of the Aristotelian Society, Supplementary Volumes, Vol. 81.


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