David Hume was a philosopher, economist, historian and essayist, who proposed the highly influential system of philosophical empiricism, skepticism and naturalism. He was skeptical about the religious beliefs and argued that religion is both irrational and impractical. He explained the importance of relation between science and the human nature. He wanted to reform moral philosophy using Newtonian methods, and was impressed of Newtonian works on natural philosophy.
From the time of Aristotle, it was believed that certain causes produce certain effects. It was assumed A causes B, where A and B are two events, and remembering any one can make us remember the other, though these two events were not experienced together. But Hume disagreed about this belief, and explained that unless we experience both the events together, one can never know that they both can occur together.
He investigated that causation leads to the context of thinking about what and how one can know about matters of fact. According to him, without any experience about an object, one could not discover its cause or effect. He defines causation as the relation between two objects or events. He claims that experience can only help us find the causal relations between the events. He made the following observation to conclude that there is a causal relation between two events:
i. Both, cause and effect should share a common border in space and time. The cause and effect should be in sequence.
ii. Both cause and effect should have a constant union, which constitutes the relation.
iii. The same effect should be arising from the same cause every time, and same effect should not arise from any other cause.