But can’t scientific laws be derived from the logical connection between cause and effect? No, Hume argued, because there is no logical connection between cause and effect. We may see event A and then event B, and we may assume that event A caused event B, but we cannot know this for sure. All we have observed is a correlation, and no number of observed correlations can add up to a necessary connection.

Consider a simple illustration. A child drops a ball on the ground for the first time. To his surprise, it bounces. Then the child’s uncle, a graduate of the Massachusetts Institute of Technology, explains to the child that dropping a round object like a ball causes it to bounce. He might explain this by employing general terms like property and causation. If these are not meaningless terms, they must refer to something in experience. But now let us consider a deep question that Hume raises: what experience has the uncle had that the child has not had? The difference, Hume notes, is that the uncle has seen a lot of balls bounce. Every time he has dropped a ball it has bounced. And every time he has seen someone else do it, the result was the same. This is the basis—and the sole basis–of the uncle’s superior knowledge.

Hume now draws his arresting conclusion: the uncle has no experience fundamentally different from the child’s. He has merely repeated the experiment more times. So it is custom or habit that makes him think, “Because I have seen this happen many times before, therefore it must happen again:’ But the uncle has not estab- lished a necessary connection, merely an expectation derived from past experience. How does he know that past experience will repeat itself every time in the future? In truth, he does not know. In this way Hume concluded that the laws of cause and effect cannot be validated. Hume is not denying that nature has laws, but he is denying that we know what those laws are. When we posit laws, Hume suggests this is simply a grandiose way of saying, “Here is our best guess based on previous tries.”