TRUTH OR DARE

Dick Pountain/Tue 16 November 2004/10:56 pm/Idealog 124

Truth sometimes feels as though it ought to be a substance rather like oil - everyone nowadays is very keen to get hold of it, but it's often in short supply. We seem to have become especially sensitive to questions of truth recently. For example was it true, or not true, that Sadam Hussein's regime possessed Weapons of Mass Destruction? Many people's lives have depended on the answer to that one (either way). Or consider the recent American election. It seems likely that the result was determined by the votes of a sizeable part of the US population that believes truth is something that's revealed by God, not by Man: say, the truth about how old the Earth is, or how so many fossils came to be lying around.

We may be fascinated by the truth, but its nature remains extremely difficult to pin down, or even to talk about in any sensible way. Part of the problem is that we mean several different things when we use the word. In everyday use truth takes on a moral aspect - it's something good, something which it's your moral duty to always to tell (supposing that you know it). If Johnny stole the last pie, and I know that he did it, then I must say so when questioned. This common sense notion of truth is hugely important: any society would rapidly descend into chaos unless most people tell this sort of truth, most of the time, about practical matters, so that others can trust them and act effectively. If I ask 'is it raining in Edinburgh', your answer may affect the way I plan to dress, and I need you to tell me truly. Much elaborated, such a version of truth forms the basis of our systems of law, justice and punishment. However it's not without many problems, what 'knowing' really means being only one of them. Perhaps I was pissed when I saw Johnny take that pie, or perhaps I mistook him for his evil twin...     

We in the IT business of course have another, rather shallower notion of truth that we use all the time, one derived from logic and in particular from the algebra invented by George Boole. Our PCs actually process truth all the time. At the physical level the content they manipulate - whether it's held in RAM, on disk, flowing over a network cable or glowing on a display screen - consists of quantities like charge, voltage or magnetisation, but at the system level where processing becomes possible, we treat these all as standing for just one of the two same values, True or False. At higher levels still we treat these in turn as encoding words, numbers, pictures or sounds. This Boolean version of truth has the enormous advantage that you can reason about it coherently: given two statements of known truth value, you can combine them and know the truth of the result. It's not a very satisfying form of truth for everyday life though. A digital camera can digitise Johnny's appearance - at a level of 'truth' to the original that depends on how many megapixels it samples - but there's no device yet that can digitise Johnny's intentions or my beliefs about them, short of us discussing them and writing them down, and once we do that we find that Boolean algebra has very little purchase on our utterances.