A Matter of Evidence

A few weeks ago, my good friend the Laird of Muc na Buccett, who is a long-time follower of the black art of philosophy, reminded me of the induction paradox. Induction, for those unfamiliar with the term, is the philosophical theory (or, on another view, the psychological process) by which we draw general conclusions from our specific experience. Thunder follows lightning. All tigers have stripes. The sun will rise tomorrow. Such truths, which constitute some of our most basic beliefs about the world we live in, are supposedly drawn from our observation of particular examples. We see a pattern or a regularity. We draw a conclusion or a hypothesis. Subsequent observations confirm our hypothesis until we gradually become more and more secure in our conviction that the belief is true.

There are a number of interesting points one can make about this common sense notion. One, which was the subject of the Laird's communication, goes like this. The statement 'All ravens are black' is confirmed by our experience. Every raven I see gives me a little more evidence, a tiny bit more confidence that the statement is true. However, the statement 'All ravens are black' is logically equivalent to 'No non-black thing is a raven.' If one is true the other is true. So whatever confirms the second also confirms the first. Note, though, that the second statement is confirmed by an observation of a green budgerigar, a grey building, or a blue sky. In fact, on this argument, every object in the world that isn't a raven and isn't black confirms the truth of the statement that 'All ravens are black.'

Going one step further, it seems that any one observation can confirm a vast number of inductive truths. A yellow banana, for example, not only confirms that ravens are black but also that motor cars have wheels, that gentlemen prefer blondes, and that George W. Bush is the most honest man on Earth. In fact, as Trevor points out, given the vast number of observations that confirm the latter hypothesis one could be forgiven for concluding that it was true (along with the proposition that George W. Bush is the biggest rogue on earth, of course). All in all it is difficult to see how we learn anything whatever from induction. Something else must be going on.

7 October 2008


















What's wrong with this? it seems fine to me.



© Chris Else 2008