Hume challenges us to consider any one event and meditate on it; for instance, a billiard ball striking another. He holds that no matter how clever we are, the only way we can infer if and how the second billiard ball will move is via past experience. There is nothing in the cause that will ever imply the effect in an experiential vacuum. And here it is important to remember that, in addition to cause and effect, the mind naturally associates ideas via resemblance and contiguity.
Hume does not hold that, having never seen a game of billiards before, we cannot know what the effect of the collision will be. Rather, we can use resemblance, for instance, to infer an analogous case from our past experiences of transferred momentum, deflection, and so forth. We are still relying on previous impressions to predict the effect and therefore do not violate the Copy Principle.
We simply use resemblance to form an analogous prediction. And we can charitably make such resemblances as broad as we want. Thus, objections like: U nder a Humean account, the toddler who burned his hand would not fear the flame after only one such occurrence because he has not experienced a constant conjunction , are unfair to Hume, as the toddler would have had thousands of experiences of the principle that like causes like, and could thus employ resemblance to reach the conclusion to fear the flame.
If Hume is right that our awareness of causation or power, force, efficacy, necessity, and so forth - he holds all such terms to be equivalent is a product of experience, we must ask what this awareness consists in. What is meant when some event is judged as cause and effect?
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Strictly speaking, for Hume, our only external impression of causation is a mere constant conjunction of phenomena, that B always follows A, and Hume sometimes seems to imply that this is all that causation amounts to. And this notion of causation as constant conjunction is required for Hume to generate the Problem of induction discussed below. Hume points out that this second component of causation is far from clear.
What is this necessity that is implied by causation? Clearly it is not a logical modality, as there are possible worlds in which the standard laws of causation do not obtain. It might be tempting to state that the necessity involved in causation is therefore a physical or metaphysical necessity. However, Hume considers such elucidations unhelpful, as they tell us nothing about the original impressions involved.
At best, they merely amount to the assertion that causation follows causal laws. But invoking this common type of necessity is trivial or circular when it is this very efficacy that Hume is attempting to discover. We must therefore follow a different route in considering what our impression of necessity amounts to. As causation, at base, involves only matters of fact, Hume once again challenges us to consider what we can know of the constituent impressions of causation.
Once more, all we can come up with is an experienced constant conjunction. Of the common understanding of causality, Hume points out that we never have an impression of efficacy. Because of this, our notion of causal law seems to be a mere presentiment that the constant conjunction will continue to be constant, some certainty that this mysterious union will persist.
Hume argues that we cannot conceive of any other connection between cause and effect, because there simply is no other impression to which our idea may be traced. This certitude is all that remains.
For Hume, the necessary connection invoked by causation is nothing more than this certainty. Instead, the impression of efficacy is one produced in the mind. Ergo, the idea of necessity that supplements constant conjunction is a psychological projection. We cannot help but think that the event will unfurl in this way. He gives similar but not identical definitions in the Enquiry. There are reams of literature addressing whether these two definitions are the same and, if not, to which of them Hume gives primacy. Robinson is perhaps the staunchest proponent of the position that the two are nonequivalent, arguing that there is an nonequivalence in meaning and that they fail to capture the same extension.
Two objects can be constantly conjoined without our mind determining that one causes the other, and it seems possible that we can be determined that one object causes another without their being constantly conjoined. But if the definitions fail in this way, then it is problematic that Hume maintains that both are adequate definitions of causation. Some scholars have argued for ways of squaring the two definitions Don Garrett, for instance, argues that the two are equivalent if they are both read objectively or both read subjectively , while others have given reason to think that seeking to fit or eliminate definitions may be a misguided project.
One alternative to fitting the definitions lies in the possibility that they are doing two separate things, and it might therefore be inappropriate to reduce one to the other or claim that one is more significant than the other. There are several interpretations that allow us to meaningfully maintain the distinction and therefore the nonequivalence between the two definitions unproblematically. For instance, D1 can be seen as tracing the external impressions that is, the constant conjunction requisite for our idea of causation while D2 traces the internal impressions, both of which are important to Hume in providing a complete account.
Another method is to cash out the two definitions in terms of the types of relation. Walter Ott argues that, if this is right, then the lack of equivalence is not a problem, as philosophical and natural relations would not be expected to capture the same extension. If the definitions were meant to separately track the philosophical and natural relations, we might expect Hume to have explained that distinction in the Enquiry rather than dropping it while still maintaining two definitions. Bennett Though this treatment of literature considering the definitions as meaningfully nonequivalent has been brief, it does serve to show that the definitions need not be forced together.
In fact, later in the Treatise , Hume states that necessity is defined by both, either as the constant conjunction or as the mental inference, that they are two different senses of necessity, and Hume, at various points, identifies both as the essence of connection or power. Whether or not Robinson is right in thinking Hume is mistaken in holding this position, Hume himself does not seem to believe one definition is superior to the other, or that they are nonequivalent.
The Law of Causality and Its Limits : Philipp Frank :
Attempting to establish primacy between the definitions implies that they are somehow the bottom line for Hume on causation. But Hume is at pains to point out that the definitions are inadequate. And what stronger instance can be produced of the surprizing ignorance and weakness of the understanding than [the analysis of causation]? But though both these definitions be drawn from circumstances foreign to cause, we cannot remedy this inconvenience, or attain any more perfect definition…. EHU 7. The tone this passage conveys is one of resigned dissatisfaction.
Although Hume does the best that can be expected on the subject, he is dissatisfied, but this dissatisfaction is inevitable. This is because, as Hume maintains in Part VII of the Enquiry , a definiens is nothing but an enumeration of the constituent simple ideas in the definiendum. It is an inconvenience that they appeal to something foreign, something we should like to remedy.
Unfortunately, such a remedy is impossible, so the definitions, while as precise as they can be, still leave us wanting something further. But if this is right, then Hume should be able to endorse both D1 and D2 as vital components of causation without implying that he endorses either or both as necessary and sufficient for causation. Though Hume gives a quick version of the Problem in the middle of his discussion of causation in the Treatise T 1. It should be noted, however, that not everyone agrees about what exactly the Problem consists in.
Briefly, the typified version of the Problem as arguing for inductive skepticism can be described as follows:. Recall that proper reasoning involves only relations of ideas and matters of fact. Again, the key differentia distinguishing the two categories of knowledge is that asserting the negation of a true relation of ideas is to assert a contradiction, but this is not the case with genuine matters of fact.
But in Section IV, Hume only pursues the justification for matters of fact, of which there are two categories:. For Hume, B would include both predictions and the laws of nature upon which predictions rest. We cannot claim direct experience of predictions or of general laws, but knowledge of them must still be classified as matters of fact, since both they and their negations remain conceivable.
In considering the foundations for predictions, however, we must remember that, for Hume, only the relation of cause and effect gives us predictive power, as it alone allows us to go beyond memory and the senses. All such predictions must therefore involve causality and must therefore be of category B. But what justifies them?
Since the Problem of Induction demands that causal connections cannot be known a priori , and that our access is only to constant conjunction, the Problem seems to require the most crucial components of his account of necessity. It is therefore not entirely clear how Hume views the relationship between his account of necessity and the Problem. This is to say that B is grounded in A. But again, A by itself gives us no predictive power.
The answer to this question seems to be inductive reasoning. We use direct observation to draw conclusions about unobserved states of affairs. But this is just to once more assert that B is grounded in A. The more interesting question therefore becomes how we do this. What lets us reason from A to B? The only apparent answer is the assumption of some version of the Principle of the Uniformity of Nature PUN , the doctrine that nature is always uniform, so unobserved instances of phenomena will resemble the observed.
This is called an assumption since we have not, as yet, established that we are justified in holding such a principle. Once more, it cannot be known a priori , as we assert no contradiction by maintaining its falsity. A sporadic, random universe is perfectly conceivable. Therefore, knowledge of the PUN must be a matter of fact. But the principle is predictive and not directly observed.
The Law of Causality and its Limits
This means that the PUN is an instance of B , but we were invoking the PUN as the grounds for moving from beliefs of type A to beliefs of type B , thus creating a vicious circle when attempting to justify type B matters of fact. We use knowledge of B as a justification for our knowledge of B. We have no ground that allows us to move from A to B , to move beyond sensation and memory, so any matter of fact knowledge beyond these becomes suspect. However, there are philosophers Max Black, R. Braithwaite, Charles Peirce, and Brian Skyrms, for instance that, while agreeing that Hume targets the justification of inductive inference, insist that this particular justificatory circle is not vicious or that it is unproblematic for various reasons.
As discussed below, Hume may be one such philosopher. Alternatively, there are those that think that Hume claims too much in insisting that inductive arguments fail to lend probability to their conclusions. Hume illicitly adds that no invalid argument can still be reasonable. Stove Induction is simply not supported by argument, good or bad. Instead, it is an instinctive mechanism that we share with animals. In the external world, causation simply is the regularity of constant conjunction.
Because of the variant opinions of how we should view the relationship between the two definitions proffered by Hume, we find two divergent types of reduction of Humean causation. Robinson, for instance, claims that D2 is explanatory in nature, and is merely part of an empiricist psychological theory.
Robinson A reductive emphasis on D1 as definitive ignores not only D2 as a definition but also ignores all of the argument leading up to it. However, this practice may not be as uncharitable as it appears, as many scholars see the first definition as the only component of his account relevant to metaphysics. For instance, D. Armstrong, after describing both components, simply announces his intention to set aside the mental component as irrelevant to the metaphysics of causation.
In addition to its accounting for the necessity of causation mentioned above, recall that Hume makes frequent reference to both definitions as accurate or just, and at one point even refers to D2 as constituting the essence of causation. Below, the assumption that Hume is even doing metaphysics will also be challenged. The more common Humean reduction, then, adds a projectivist twist by somehow reducing causation to constant conjunction plus the internal impression of necessity. Largely for this reason, we have a host of reductionist interpretations rather than a single version.
The unifying thread of the reductionist interpretations is that causation, as it exists in the object , is constituted by regularity. After all, both D1 and D2 seem reductive in nature. If, as is often the case, we take definitions to represent the necessary and sufficient conditions of the definiendum, then both the definitions are reductive notions of causation. D1 reduces causation to proximity, continuity, and constant conjunction, and D2 similarly reduces causation to proximity, continuity, and the internal mental determination that moves the first object or idea to the second.
Therefore, the various forms of causal reductionism can constitute reasonable interpretations of Hume. By putting the two definitions at center state, Hume can plausibly be read as emphasizing that our only notion of causation is constant conjunction with certitude that it will continue. One way to interpret the reasoning behind assigning Hume the position of causal skepticism is by assigning similar import to the passages emphasized by the reductionists, but interpreting the claims epistemically rather than ontologically.
If it is true that constant conjunction with or without the added component of mental determination represents the totality of the content we can assign to our concept of causation, then we lose any claim to robust metaphysical necessity. But once this is lost, we also sacrifice our only rational grounding of causal inference.
Our experience of constant conjunction only provides a projectivist necessity, but a projectivist necessity does not provide any obvious form of accurate predictive power. Hence, if we limit causation to the content provided by the two definitions, we cannot use this weak necessity to justify the PUN and therefore cannot ground predictions. We are therefore left in a position of inductive skepticism which denies knowledge beyond memory and what is present to the senses.
By limiting causation to constant conjunction, we are incapable of grounding causal inference; hence Humean inductive skepticism. Since we never directly experience power, all causal claims certainly appear susceptible to the Problem of Induction.
The attempted justification of causal inference would lead to the vicious regress explained above in lieu of finding a proper grounding. There are, however, some difficulties with this interpretation. For instance, the Copy Principle, fundamental to his work, has causal implications, and Hume relies on inductive inference as early as T 1. Of course, if this is the correct way to read the Problem of Induction, then so much the worse for Hume. It is more comfortable to the ordinary wisdom of nature to secure so necessary an act of the mind, by some instinct or mechanical tendency, which may be infallible in its operations, may discover itself at the first appearance of life and thought, and may be independent of all the laboured deductions of the understanding.
As nature has taught us the use of our limbs, without giving us the knowledge of the muscles and nerves by which they are actuated; so she has implanted in us an instinct, which carries forward the thought in a correspondent course to that which she has established among external objects; though we are ignorant of those powers and forces, on which this course and succession of objects totally depends.
EHU 5. Here, Hume seems to have causal inference supported by instinct rather than reason. The causal skeptic will interpret this as descriptive rather than normative, but others are not so sure.
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It is not clear that Hume views this instinctual tendency as doxastically inappropriate in any way. However, it is not reason that justifies us, but rather instinct and reason, in fact, is a subspecies of instinct for Hume, implying that at least some instinctual faculties are fit for doxastic assent. This will be discussed more fully below. Against the positions of causal reductionism and causal skepticism is the New Hume tradition.
However, the position can be rendered more plausible with the introduction of three interpretive tools whose proper utilization seems required for making a convincing realist interpretation. Of these, two are distinctions which realist interpretations insist that Hume respects in a crucial way but that non-realist interpretations often deny. The last is some mechanism by which to overcome the skeptical challenges Hume himself raises. The first distinction is between ontological and epistemic causal claims.
Strawson points out that we can distinguish:. It simply separates what we can know from what is the case. This undercuts the reductionist interpretation.
Simply because Hume says that this is what we can know of causation, it does not follow that Hume therefore believes that this is all that causation amounts to. If Hume were a reductionist, then the definitions should be correct or complete and there would not be the reservations discussed above. In fact, Hume must reject this inference, since he does not believe a resemblance thesis between perceptions and external objects can ever be philosophically established. The epistemic interpretation of the distinction can be made more compelling by remembering what Hume is up to in the third Part of Book One of the Treatise.
Here, as in many other areas of his writings, he is doing his standard empiricist investigation. Since we have some notion of causation, necessary connection, and so forth, his Copy Principle demands that this idea must be traceable to impressions. Thus, it is the idea of causation that interests Hume.
In fact, the title of Section 1. Mounce 32 takes this as indicative of a purely epistemic project. Although this employment of the distinction may proffer a potential reply to the causal reductionist, there is still a difficulty lurking. While it may be true that Hume is trying to explicate the content of the idea of causation by tracing its constituent impressions, this does not guarantee that there is a coherent idea, especially when Hume makes occasional claims that we have no idea of power, and so forth.
This is to posit a far stronger claim than merely having an idea of causation. The realist Hume says that there is causation beyond constant conjunction, thereby attributing him a positive ontological commitment, whereas his own skeptical arguments against speculative metaphysics rejecting parity between ideas and objects should, at best, only imply agnosticism about the existence of robust causal powers. It is for this reason that Martin Bell and Paul Russell reject the realist interpretation. However, if the previous distinction is correct, then Hume has already exhaustively explicated the impressions that give content to our idea of causation.
This is the very same content that leads to the two definitions. It seems that Hume has to commit himself to the position that there is no clear idea of causation beyond the proffered reduction. But if this is true, and Hume is not a reductionist, what is he positing? It is here that the causal realist will appeal to the other two interpretive tools, viz. The general proposal is that we can and do have two different levels of clarity when contemplating a particular notion.
Groups compiled by relating these simple ideas form mental objects. In some cases, they combine in a coherent way, forming clear and distinct complex ideas, while in other cases, the fit is not so great, either because we do not see how the constituent ideas relate, or there is something missing from our conception. These suppositions do not attain the status of complex ideas in and of themselves, and remain an amalgamation of simple ideas that lack unity.
The claim would then be that we can conceive distinct ideas, but only suppose incomplete notions. Something like this distinction has historical precedence. In the Fifth Replies, Descartes distinguishes between some form of understanding and a complete conception. The realist employment of this second distinction is two-fold. First, the realist interpretation will hold that claims in which Hume states that we have no idea of power, and so forth, are claims about conceiving of causation. They only claim that we have no clear and distinct idea of power, or that what is clearly and distinctly conceived is merely constant conjunction.
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But a more robust account of causation is not automatically ruled out simply because our notion is not distinct. In this way, the distinction may blunt the passages where Hume seems pessimistic about the content of our idea of causation. The second step of the causal realist interpretation will be to then insist that we can at least suppose in the technical sense a genuine cause, even if the notion is opaque, that is, to insist that mere suppositions are fit for doxastic assent. To return to the Fifth Replies, Descartes holds that we can believe in the existence and coherence of an infinite being with such vague ideas, implying that a clear and distinct idea is not necessary for belief.
Hume denies clear and distinct content beyond constant conjunction, but it is not obvious that he denies all content beyond constant conjunction. This second distinction is not introduced without controversy. Kail, 60 There, Hume describes a case in which philosophers develop a notion impossible to clearly and distinctly perceive, that somehow there are properties of objects independent of any perception. We simply cannot conceive such an idea, but it certainly remains possible to entertain or suppose this conjecture.
Ott Even granting that Hume not only acknowledges this second distinction but genuinely believes that we can suppose a metaphysically robust notion of causal necessity, the realist still has this difficulty. How can Hume avoid the anti-realist criticism of Winkler, Ott, and Clatterbaugh that his own epistemic criteria demand that he remain agnostic about causation beyond constant conjunction? In the classical world we live in, it comes with a few basic assumptions. The first big rule of classical causality is that things have causes.
Second, effects follow causes in a predictable, linear manner. You swing your leg, make contact with the ball, and off it moves, in that order and no other. Third, big effects grow up from little causes. A piston, for example, starts to move when a lot of individual hot atoms hit against it and push it a certain way. The laws of thermodynamics , which govern the way atoms move, then provide certain rules about what causes can precipitate what effects, and so an overall direction for causality — a flow of time.
Modern science presents a number of challenges to this naive view of causality. Time is warped by the presence of large masses or when travelling at high speed, and passes at different rates for different observers. Even so, relativity bends over backwards to maintain a sensible conception of cause and effect as we know it. The key is the speed of light, which relativity insists is a constant. It represents the maximum speed that any influence can travel in the universe.
As an example, if the sun were suddenly to explode, the effect of frying Earth to a cinder would not happen instantaneously. Earth would have just over eight minutes of peaceful life still left — the time it takes light to travel from the sun — before it got intimation of the oncoming calamity. Unfortunately, matters of cause and effect get distinctly murkier in the other realm of modern physics, the quantum world.