Truth sometimes feels as if it’s a substance rather like oil – everyone is very keen to get hold of it, but it’s often in short supply. We seem to be becoming especially sensitive to questions of truth in recent years. For example, was it true, or not true, that Saddam 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 decided by the votes of that sizeable chunk of the US population that believes truth is something revealed by God, not by Man: for instance, 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 a good, something which it’s your moral duty 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 of its people told this sort of truth, most of the time, about practical matters, so that others could 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 truthfully. Much elaborated, such a version of truth forms the basis of our systems of law and justice. However, it’s not without many profound problems, and what ‘knowing’ really means is only one of them. Perhaps I was drunk when I saw Johnny take that pie, or perhaps I mistook him for his evil twin.

In the IT business we 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. In one sense our PCs are actually machines for processing truth. The content they manipulate – whether it’s held in RAM, on disk, flowing over a network cable or glowing on a display screen – consists at the physical level of quantities like charge, voltage or magnetic flux, but at the system level where processing happens we treat these all as standing for just one of the same two values, True or False. This 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 if the result is true.

It’s not a very satisfying form of truth for everyday life, though, as it can only really cope with the appearances of the world – that which can be easily digitised. A digital camera might capture Johnny’s face, 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 Boolean Algebra of very little use. There’s a deeper problem with Boolean truth too, which Alan Turing discovered. Write a program that will halt if a certain proposition is true: if the program doesn’t halt, that could be because the proposition is false, or because you haven’t waited long enough (and how long would be long enough?). Truth isn’t really graspable by computation.

The philosophy profession has of course devoted a great deal of effort to pinning down truth, but philosophers’ conclusions are eminently put-downable for most casual readers. If you’ve read Kripke, Putnam and Quine then you’ve suffered enough already, so it’s just as well I don’t have room here for any grisly details. No, the only theory of truth that’s ever tickled my fancy is the naturalistic one, which holds that there is indeed an Absolute Truth, and that it consists simply of the total configuration of all the particles (without prejudging what these might be) that make up the Universe, at every moment from the Big Bang all the way into the future and the Big Whimper. This is rather a large concept, in fact the largest concept there could ever be. It’s so big that nothing or no-one could ever know it. It’s so big that you may believe, as I do, that it leaves no room for God, or you may prefer to believe with Spinoza that it ‘is’ God.

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