Hume famously presents the problem of induction throughout his two major works, A Treatise of Human Nature and An Enquiry Concerning Human Understanding. Hume presents his arguments in the context of his main project of analyzing the operations of rational agents and how they arrive at common sense conclusions, such as ‘tomorrow the sun will rise.” In pursuit of this goal he focuses mainly on causal reasoning and its foundation, inductive reasoning. He questions the rational validity of forming general conclusions given only specific past experience or evidence. He concludes that there is no rational basis for induction and correspondingly causal reasoning. However, as he sets forth these arguments against induction he seems reluctant to reject causal reasoning as a matter of practical action. He provides context to his arguments that seem to position him away from the strict skepticism that his arguments on induction represent a face value. There remains lively modern discussion about what kind of skepticism did Hume align himself with in regards to causal reasoning. This essay will argue that Hume is a skeptic on induction in the sense that he rejects it logically, show that he ultimately embraces a line of action against his logical beliefs, and present some caveats to this embrace. I will begin by going over the structure of Hume’s arguments against causal reasoning and explain the ways in which they initially seem skeptical. I will then show some evidence of Hume taking a more moderate posture towards induction and conclude by attempting to show some reconciliation between the two sides and its issues.
Hume’s presentation of the problem of induction is within the context of a conversation surrounding causal inferences, the ability to connect a present set of experiences to something larger. He considers two methods through which a rational agent could conduct this operation. The first is through ‘the understanding,’ which he means as through a priori reasoning or potentially as priori reasoning plus knowledge of sensible qualities. Regarding the first of these subpoints, he rejects that anyone can arrive at the effect of an object simply through a priori reasoning. If one was to consider an object and only the ideas of it that were formed a priori, one could not imply the existence of another object. If they were able to draw this connection, it would be tantamount to necessarily having knowledge of another object from the a priori knowledge of the original object. If one object implies the knowledge of another, considering the original object means one must simultaneously be considering the other implied object. Since distinct objects have to be able to be considered separately, it is impossible for the idea of one object to imply the existence of another.
Hume also rejects a priori reasoning in addition to experience of an object’s sensible qualities as a rational basis for causal relations. When one reasons demonstratively about an object they must consider the idea of the object independent of any past experience with how the object operates. From this position of almost a total lack of knowledge, they could not possibly arrive at the effect of the object. For example, if one were to consider an aspirin so that they would only have an idea of its sensible qualities like size and shape, they could not conclude that the effect of an aspirin is to reduce headaches. Nothing about the qualities of being white, round, circular, and smooth ties the object of an aspirin to its power of curing headaches. After dispelling a priori reason as a possible avenue for causal reasoning, Hume moves to examine the only remaining option: casual connections being based on matters of fact.
Hume constructs a framework that the inner operations of causal reasoning must meet in order for them to be considered rationally sound. We can only believe in the truth of a proposition if “the state of affairs which it describes” can be connected back to our present or past experiences (Ayer, Probability and Evidence 1). This connection that Hume requires ultimately can not be met. Inductive reasoning usually occurs from repeated experiences where similar objects consistently produce other similar objects. One can examine all past experiences with either object and discover that they always exist in constant conjunction with each other. The consistent wedding of these objects convinces the agent to conclude that one is the cause and the other the effect. The existence of one object implies the existence of the other; in all future instances the expectation is that they will continue to exist in constant conjunction. For example, if throughout your life you have encountered fire multiple times. Everytime you experience fire, you feel that it produces heat. You come to the conclusion that there is a causal relationship between fire and heat.
The issue that Hume points out is that there is no reason to believe that your conclusions from your previous experiences of something apply to the future case or as Hume puts the counter position, “instances of which we have no experience must resemble those of which we have had experience” (Treatise 1.3.6). Hume first rejects that the mere existence of something can imply that it has the power to produce something else. But even if we were to ignore that objection and assume that objects have the power of production, our past experience of the objects in question only allow us to conclude that they possess a very limited sense of power. Our previous experience of an object producing another object actually just means that that specific instance of the object had the power of production in that moment. Nothing about that proposition is generalizable to the general case or the future case. That experience or however many experiences similar to it only provide proof of the object’s power of production in the moment “but can never prove that the same power must continue in the same object or set of sensible qualities” (Treatise 1.3.6).
Inorder to connect these various past experiences to the future, we require an additional premise; that the future will be like the past. We will call this premise the uniformity principle. For people to have rational causal reasoning based on induction, there needs to be a sound logical foundation for this uniformity principle. Hume examines some possible sources of justification. He says that it cannot be based on demonstrative reasoning, since the negation of the principle provides no clear logical contradiction. It seems perfectly plausible to conceive of a world where the future does operate in the same manner as the past. You could easily imagine holding your hands up to a fire and feeling coldness. Since we can conceive of it, it does not represent a logical contradiction. The other type of reasoning which Hume considers is ‘moral’ arguments from experience. Past experience might be able to inform us on how objects acted in the past, but it cannot lead us to any conclusions beyond that. The only way past experiences could inform us of broader conclusions about the powers of objects in general or in the future is if we assumed that the past and future will proceed uniformly but that is exactly the principle that we are trying to prove. Assuming the principle of uniformity inorder to prove the principle through ‘moral’ reasoning is circular. Since demonstrative and moral reasoning are the only two types of reasoning to Hume, he concludes that people are not able to connect past experiences to conclusions about the future. As a result, there is no logical basis for causal reasoning. If we were to define a skeptic about an issue as someone who does not find that there is sufficient evidence to show that something is true, then the arguments just layed out position Hume as a skeptic on inductive reasoning. He believes that the conclusions arrived at through causal reasoning are only probable conclusions, or statements that are less than certain.
While Hume’s concrete argumentation seems to explicitly position him as a skeptic on the issue of induction and causal reasoning, other parts of Hume’s works portray his view on common sense reasoning as more sympathetic. One noteworthy passage begins with Hume’s proposal of a proposition that naturally extends from his arguments on induction. He claims that any object which we think we have knowledge of can actually be reduced to a statement of which we have zero belief or evidence. Hume states that all knowledge resolves into probability, as it is ‘of the same nature with that evidence, which we employ in common life’ (Treatise 1.4.1). Hume proposes that for any object there are two initial stages of judgement. The first stage of judgement is from the impression of the nature of the object itself and the second stage of judgement corrects the first and is from ‘the understanding’ of the person performing the judgement. The second stage of judgement can be considered an evaluation of the strength of personal confidence in the original proposition. People of wisdom would confer a higher level of probability to the original judgement than people who lack wisdom. This operation can be applied further, as in this evaluation of personal confidence there may be a deeper evaluation of people’s ability to perform the first degree evaluations. This worry would amount to someone thinking about how they have erred in the past when they have believed something to be true, so now they are less than 100 percent sure about their belief. It is the same operation performed in the second stage judgements just with the second stage judgements as the objects in question. This judgement can continue to be made of each lower level judgement. Since people can not be absolutely certain in their faculties of judgement, every additional evaluation confers an additional probability of less than one to the chain of probabilities. Since the chain of judgements can go on infinitely so do the chain of probabilities. All pieces of knowledge are reduced to having a probability of zero, basically as if we knew nothing about them at all.
Hume only presents this argument to reject it and in a sense affirm his leanings towards a weaker form of skepticism. He believes that neither him nor anybody else could sincerely and constantly believe the argument he lays out. He equates the human ability to judge to the ability to eat or feel in the sense that we only have a limited sense of choice in the manner we conduct these actions. We are limited by some imposition by nature. He presents the arguments against induction only to sway the reader’s logical faculties, but he acknowledges that this aspect is not the sole governor of human conduct. He describes how one could present his previous argument about continually diminishing evidence through infinite probabilities to any individual and they could find no logical error in his argument, ‘yet he will continue to believe, and think, and reason as usual’ (Treatise 1.4.1). Crucially, that dynamic proves the individual’s conception of reason and belief can not be swayed by mere ideas. Ultimately Hume’s mission in this section is to moderate and provide context to his arguments against induction. He assures the reader that the aim of his arguments on induction are limited in scope and that potentially reason is not the only valuable faculty. Hume wants to clarify that he is ‘not one of those sceptics who hold that all is uncertain.’
In fact, he even proposes a different formulation of his previous theory to provide a possible avenue for people to retain a certain level of belief despite the infinite chain of diminishing probabilities. He tries to accomplish this task by introducing another variable into the argument, the level of strain put on the mind. In the case of these multi-layer judgment operations, the mind has difficulty moving from premise to premise and its ‘attention is on the stretch’ (Treatise 1.4.1). Additionally, the impression from objects is dulled compared to when the mind is at ease. The combination of these factors results in the mind not being governed by the previous principles of judgment. Since the mind is being diverted from its natural course so are the effects of principles. As a result, an individual does follow the course of logical reasoning as they might normally and do not have to accept the worthlessness of the original proposition. While this argument seems to be more of a descriptive account of why people still think they have knowledge rather than one that says that that belief is correct. Hume’s formulation of this possibility seems to show his more moderate stance towards their position as he does not want to outright criticize their irrational operations. He, instead, explains why they do so in a sympathetic way. This argument can be viewed as a push back against skepticism in its full extent. Hume’s attitude in this section is evidence that he is more sympathetic to common sense causal reasoning than appears just from his concrete arguments on induction.
Initially through his argument about induction, it seems as if Hume is a strong skeptic of causal reasoning and our ability to reason based on matters of fact. I have shown that in other places, Hume has moderated his view or taken an approach to describing his skepticism that might lead a reader to conclude that he is not a skeptic in the traditional sense. Even if he fits somewhere along the spectrum of skepticism it seems clear that his own arguments have not won the battle for his heart. He is not emotionally convinced by his logic. There certainly exists a tension between Hume’s different dispositions on induction.
Hume, in the conclusion of Book 1 of the Treatise, provides us a way, not quite to reconcile his views, but to clarify how their dynamic plays out. In this section, Hume reflects on his arguments and how they interact. He starts by setting forth a psychological claim in regards to how the human mind operates. He affirms that people do not draw causal conclusions from a combination of experience and a principle of uniformity that can be logically justified. The basis for their causal reasoning is, instead, through experiences and an expectation that the future will be similar to the past through habit. These concepts together create a more lively image in the minds of people, then the logical arguments Hume sets proposest. Hume accepts that every time someone reasons causally they are performing a fallacious mental action, but he doesn’t immediately think that that transgression is necessarily unwarranted. He immediately asks how much should ‘we yield to these illusions’ (Treatise 1.4.7). Such a question seems to illustrate that he is willing to accept some concession to irrational thoughts.
He balances the two extremes of accepting all trivial propositions and accepting only what can be solidly proven from deductive reasoning. If we were to adopt the principle that we never accept refined deductive reasoning then we must reject all of science and most of philosophy as they are built up on the logical fallacy that Hume has talked about extensively. If we were to do the opposite and accept any and all fancies of the imagination as truth then we would not have any reasoning at all.
Hume continues once again to affirm the idea that the acceptance of skepticism is fundamentally against human nature. If one were to accept skepticism, they would fall into a deep pit of questions surrounding the causes for existence, and questions about every quality of the physical world for they could not have definite knowledge of any of it. Hume seems to say that he ‘yield[s] to the current of nature’, not as a philosophical choice but one that as a human he is coerced into making. Yet in the same statement that he eschews his skeptical principles, he accepts them in perhaps the clearest way he does in the whole Treatise. He refers to them as ‘my sceptical disposition and principles,’ seemingly taking full possession of them (Treatise 1.4.7).
The clearest interpretation of Hume’s skepticism requires that we create two categories of skepticism. The first type we can call rational skepticism. This category refers to skepticism in regards to the lack of sufficient logical evidence to believe in something. The word ‘believe’ in this case is concretely connected to what can be logically arrived at from deductive reasoning plus real world experience. The other type of skepticism we can call actuated skepticism, which is the acceptance of logical skepticism but also the adoption of that skeptical mindset into how a person approaches their everyday life.
Hume is very clearly a skeptic in the rational skepticism sense. He states convincingly in his main line of argumentation but also repeats throughout the Treatise his rejection of induction on deductive grounds. On the other hand, Hume is not a skeptic in the actuated skepticism sense but perhaps to a less clear degree than he is a rational skeptic. When approached with this confrontation between his logical conclusions and his ‘non logical’ beliefs, Hume acts upon the latter. He states that ‘human nature is the only science of man’ and that he wishes to bring its appreciation more into fashion. Even more clearly he resolves ‘never more to renounce the pleasures of life for reasoning’ (1.4.7). This statement can definitively be read as a denunciation of acting off of rational skepticism and subjecting oneself to the unpleasantness that follows from that.
While Hume seems to make these strong statements at the conclusion of Book 1, accepting that he will not act upon his logical conclusions, I think these statements are not entirely genuine. His laborious and extensive efforts to reconcile and explain the two competing sides of his being is evidence that his logical skepticism stills nags at him. He claims to have sidestepped the issue by simply accepting and championing human nature, but his descriptions of the unhappiness that washed over him when he engaged with his logical arguments do not appear to be so easy to run away from. The fact that they were able to reduce him to such a state of despair shows how strongly he holds his criticism of induction rationally. In fact, it represents a specific instance in which Hume allows his beliefs on rational skepticism to materially affect his life. Just as Hume says one can not be totally confident in propositions because of self doubt, he cannot be totally confident in his choice to yield to nature. Some proportion of the time, Hume will fail to live up to his happy go lucky acceptance of human nature and succumb, perhaps only temporarily, to actuated skepticism. Ultimately Hume is not an actuated skeptic, but this position is not as strong as it can be taken to be on face value.
Hume presents a famous set of arguments against causal reasoning and its foundation of inductive reasoning. To these ideas, Hume immediately adopts a rational skeptical position. Throughout Book 1 Hume slowly moves away from embracing this skepticism in its totality. At first, rejecting the notion that we can have no certainty or belief about anything and eventually going so far as to be content with acting in contradiction to his logical beliefs. This last move, however, is not as simple or clean as he presents it and his logical beliefs can sometimes rear their ugly heads in the manner he acts as well.