In order to go beyond the objects of human reason, Hume proposed that reasoning was based upon cause and effect. Fundamental relations help us to know things beyond our immediate surroundings. All of our knowledge is based on experience. Therefore, we need experience in order to reach relationships of the world and experience constant conjunction. Hume stated that he "shall venture to affirm, as a general proposition which admits no exception, that the knowledge of this relation is not in any instance, attained by reasonings "a priori", but arises entirely from experience." Unfortunately, our experience of constant conjunction only tells us about the past. Rationally, that is all it tells us. We can expect the effect to follow the cause, but it is not a sufficient basis to assume the effect will come from the cause in the future. .
Hume asserted that the future will resemble the past. This is the assumption underlying all our ideas of causality. If the future does not resemble the past, then all our reason based on cause and effect will crumble. Hume demonstrates that it is not a relation of ideas that future will resemble the past; it is possible that the course of nature will change. Therefore, what happens in the future is neither a relation of ideas, nor a matter of fact. It is impossible, therefore, that any arguments from experience can prove this similarity of past to future, since all these arguments are founded on the belief of that resemblance.
Now Hume proposed that all inferences come from custom, not reasoning. Through custom or habits, we have become accustomed to expect an effect to follow a cause. This is not a rational argument. This argument centers on the theory of constant conjunction, which does not fall under either fork of reason. All inferences from experience, therefore, are effects of custom, not reasoning.
Hume analyzed the idea of causality by emphasizing the three demands that can be verified through observation.
