If I were an electrician and I infer that the electrical circuit leading to the bulb was “hot”, then I must doing the job on a house for a while, thus learning it from my experience. According to Hume, we cannot make that causal relation assumption because there are many things happen at the same time when the bulb was “hot”. We cannot reason the causality between any independent event. However, everyone of us make associations between things all the time because we learn from past experiences. Hume does think that the causal relation exists, but it is beyond human comprehension.
We born with no ideas, with nothing, then we get the perceptions of the mind, which is divided into two classes or species by Hume: thoughts or ideas and impression. The difference between the two being by marked by a difference of “forcefulness” and “vivacity”, so that impressions relate roughly to “feeling” (or “sensing”) and ideas to “thinking”. “By the term impression, then, I mean all our more lively perceptions, when e hear, or see, or feel, or love, or hate, or desire, or will.”(II 3) Hume divides impressions into those of “sensation” and those of “reflection”. Impressions of sensation derive from our senses, impressions of reflection derive from our experience of our mind, for example, feeling emotions. Ideas are copies of impressions of the first few times we sense something, but “less forcible and lively”. They are what arise when we reflect upon our impressions, so the memory of seeing the color red or a thought about anger are considered ideas. In section III Of the Association of Ideas, Hume discusses the connections that exist between ideas, asserting that all ideas are linked to other ideas.
Hume lays out three principles by which ideas might be associated: resemblance (where a picture of a tree might make us think of the tree), contiguity in time or place (where mention of one apartment might lead us to discuss others), and cause and effect (where the thought of a wound makes us think of the pain that follows from it) (III 3). We use those associations all the time without truly prove their validity. Assuming the bulb is “hot” by seeing a light on is a problem of induction on causality.
We cannot form any conception at all on the world without causal relations between the things, but the cause we discover is something we cannot actually observe. We may say that the eventA causes eventB, but we find when we examine the situation that all we observe is that the eventA followed by eventB. There is some third entity in the situation: a causal link between them that we observe. And when it came to say that we know that the eventA is the cause of eventB because B always the event follow event A because of the fact is, for example, the day always there followed by the night and the night always is there follow the day, but neither is the cause of the other. The two events are separated. Correlation doesn’t imply causation. Moreover, the nature may change. “That there are no demonstrative arguments in the case, seems evident; since it implies no contradiction, that the course of nature may change, and that an object, seemingly like those which we have experienced, may be attended with different or contrary effects”(IV II 5). So we cannot make any assumptions on anything that could be changing. So we have this indispensable notion of cause, which is our hard conception of the world and our understanding of our experience and yet this notion is not validated by experience or observation and it can’t be validated by logic either.
Hume then asks how we know the principle of cause and effect: if I see one billiard ball rolling toward another, how do I know that the second ball will move when it is struck? He suggests that this knowledge cannot be a priori, since I can deny that the second billiard ball will move without contradiction. Cause and effect are themselves totally distinct: nothing in the movement of the first billiard ball can a priori suggest to me the movement of the second billiard ball. Hume thus concludes that our knowledge of cause and effect must be based on experience. From observed phenomena in the past we infer as yet unobserved phenomena in the future.
We base our knowledge of future events in past experience, but how do we know that the past is a good guide for future predictions? Hume distinguishes between “demonstrative reasoning,” which is based on relations of ideas, and “moral reasoning,” which is based on matters of fact. We cannot know that the future will resemble the past by means of demonstrative reasoning, since there is no contradiction in suggesting that the future will not resemble the past. Moral reasoning is also unhelpful, since it falls into a vicious circle. If all our predictions about the future are based on this principle–that the future will resemble the past–and that principle is derived from past experience, we cannot know that it will remain true in the future except by assuming that principle from the outset.