Ciara asked:

What is Hume’s sceptical argument about induction?

Answer by Tony Fahey

David Hume was one of the first philosophers to point out the problem of induction. To accept an inference on the evidence that it has worked well in the past is illogical. One cannot infer a universal proposition from a particular one. While many of the scientific conclusions are drawn from this method we know from logic that an inductive inference is illogical and irrational. Thus, we can conclude that the success of science is based on a fallacious inference. This is known as the ‘scandal’ of science.

In inductive inferences we infer universal principles from particular ones. Scientists use the inductive method to justify or confirm their findings, or hypotheses. However, as Hume argues, since we cannot rationally infer ‘all propositions’ from particular propositions, scientific findings are always unsound – hence we have the scandal of science. John Stuart Mill held that the solution to this problem was to turn inductive inferences into deductive inferences. He did this by introducing a major universal premise, or ‘first principle’, into the inductive process. This major universal premise is the Principle of the Uniformity of Nature. That is, because something has always been the case in the past, we suppose that it will always be the case in the future. Moreover, because something occurs in a particular space or time in the universe, we can take it that the same principle will apply in all regions of space and time. In short, because nature is uniform, a causal relationship which holds in one place holds in all cases. For example, because the universe is causally uniform, we can take it because we know that heat causes copper to expand here in Ireland, we can take it that this principle holds throughout nature.

There are two weaknesses in this argument. First, how do we know that the premise is true? That is, how do we know that that which occurs in one region of space will occur throughout nature? Secondly, even if we accept that it is the case, the argument is not deductively valid. For it cannot be said that the Principle of Uniformity of Nature is self-evident truth. While it might be argued that evidence shows it to be the case, we know that empirical evidence is not deductive but inductive, and, as Hume has shown, as such it cannot be proven to apply at all times or in all cases.