It is not just religious maniacs who believe in the truth. It is deeply embedded in the world view of science, of common sense, and even fields of academic inquiry which see themselves as being hostile to what they perceive as science. The truth rules supreme everywhere, or so it seems.
But what is truth? When we say something is true we usually mean, I think, that it corresponds to reality – the so-called correspondence theory of truth. But what is reality, and how can human ideas “correspond” to it? Surely human ideas are a completely different type of thing from reality, so what sense does the idea of correspondence make? Perhaps what we see as the truth is part of a dream, or part of a way of seeing the world we make up in collaboration with other people – as the social constructivists would have us believe? This latter perspective seems obviously true (whatever that may mean!) to me - but this may just be the dream into which I've been socialized.
However, let’s accept the idea of truth and try to guess where it might have come from? If we accept the theory of evolution by natural selection, the answer is simple: the idea of truth helped our ancestors survive. A belief in the truth about lions and cliffs helped our ancestors avoid being eaten by the former and falling off the latter. The idea of a fixed reality, which we can apprehend and see as the truth, is obviously a very powerful tool for living in the everyday world. People who did not believe in the reality of lions and cliffs would not have survived to pass on their genes.
This implies that the idea of objective reality and the assumption that we can apprehend the truth about it is merely a human convenience. Frogs or intelligent aliens would almost certainly view the world in very different ways; what we see as truth and what they see as truth would, I think, be very different.
Most statements in ordinary languages presuppose the idea of truth. When I say that Sally was at home at 10 pm on 1 August 2014, I mean that this is a true statement about what happened. Further, if Sally is suspected of murdering Billy 50 miles away at 10 pm on 1 August 2014, then if it's true that she was at home then it can't be true that she murdered Billy. She can only be in one place at one time - "obviously". Ideas of truth, and the "objective" reality of objects in time and space, and the fact that one object can only be in one place at one time, are all bound up in our common sense world view. It is almost impossible to talk in ordinary language without assuming the truth of this world view - it is just "obviously" true.
However the concept is truth is often taken far beyond everyday comings and goings of everyday objects. So we might say that it is true that God exists, that all water molecules comprise two hydrogen and one oxygen atoms, that married people are happier than unmarried people, and that the solutions of the equation x2+1=0 are x=+i and x=-i.
The difficulty is that, outside of the realm of everyday experience, the notion of truth is actually rather vague, may be difficult to demonstrate conclusively, and may come with implications that are less than helpful. Short of taking the skeptic to meet God, demonstrating his existence is notoriously difficult. We can't "see" molecules of water in the way we can see Sally at home, so the truth about water molecules needs to be inferred in other ways. Saying that the married are happier than the unmarried is obviously a statement about averages - there will be exceptions - and it also depends on what is meant by "happier". And mathematical statements are statements about concepts invented by mathematicians: applying the word true is obviously stretching the concept considerably. It is all much less straightforward than the truth that Sally was at home at 10 pm on 1 August 2014.
The idea of truth has a very high status in many circles. Saying you are seeking the truth sounds unquestionably praiseworthy. If you say something is true, then obviously you can't argue with it. Truth is good so we like to apply the concept all over the place. I'll refer to this assumption that the idea of truth, and the inevitably associated idea of an objective reality with solid objects persisting through time, apply to everything, as the cult of the truth. This notion is rather vague in terms of the assumptions about reality that go hand in hand with the idea of truth - but this is inevitable as the idea of truth gets extended further and further from its evolutionary origin. Cults, of course, depend on vagueness for their power, so that the cult's perspective can be adjusted to cater for any discrepancies with experience.
Does the cult of the truth matter? Does it matter that the idea of truth is extended far beyond its original focus? Let's look at some different areas of knowledge.
Some of the conclusions of modern physics contradict the implicit assumptions of the cult of the truth. At very small scales things can be in two places at once, and reality only makes sense in relation to an observation; for observers at high speeds measurements of physical processes are different, and the notion of things happening at a particular time depends on the motion of the observer. This all does considerable violence to everyday assumptions about reality, but physicists would simply that these are outdated and that their notion of reality is more sophisticated. It seems to me as a non-physicist, that these theories have sabotaged the idea of the truth about an objective reality beyond repair. I am reading Brian Greene's book, The hidden reality, about parallel universes, but I can't take the idea of truth seriously in relation to universes hovering out of reach which we will never, ever, be able to see in any sense. The hypothesis that the book seems to be driving towards is that we are living in a simulated world devised by Albert Einstein whose theory of general relativity seems to underpin everything.
Does this matter? Probably not for physics. The illusion of the quest for the truth about everything is probably necessary to keep physicists motivated. But in the wider sphere it is worrisome if naive and outdated ideas of physics underpin other disciplines.
The idea of truth is best regarded as a psychological convenience - usually necessary, often useful, but occasionally a nuisance. Am I claiming this statement itself is true? Of course not! My argument obviously undermines itself. But I do think it’s a useful perspective.
Beyond the rarefied world of modern physics the cult of the truth does create problems. Perhaps the most serious is that the status of truth (and science and the study of objective reality) undermines important areas which can't be incorporated into the cult of the truth. The ultimate aim of many social sciences is to make the world a better place in the future. We might, for example, be interested in making workplaces happier. The idea of truth fits comfortably with the obvious first stage of such a project - to do a survey to find out how happy workers are at the moment, and what their gripes are. The obvious things to do next would be to look at what the workers want, at what they value, and try to design workplaces to fit these requirement. This seems a more important part of the research than the initial survey, but value judgments, and the design of possible futures, do not fit neatly with the cult of the truth. So they are not taken as seriously as they should be. Most of the thought and work goes into studying the past, and the more important issues of working out what people want and how to design a suitable future, tends to get ignored. OK, so the idea of truth could be extended to include these, but only by bending it so that it gets stupid; the cult of the truth tends to deflect our attention from the problem of designing futures.
In fact the situation is even worse than this because the truths studied in many social science tend to be of rather limited scope. So we study how happy people are in particular organizations at particular times. So what? Everyone knows the situation may be very different elsewhere. The truths studied by physicists are assumed to apply everywhere throughout time (although this can be challenged over billions of years or light-years), but the truths of many social sciences are very parochial. The cult of the truth restricts our attention to trivial questions, dismisses the big questions as trivial because the idea of truth does not apply.
There are further unfortunate side effects from taking truth too seriously. If we have one theory which is deemed true, this may be taken to imply that other theories covering the same are assumed to be false. This may be too restrictive: there could be different ways of looking at the same thing, some of which may, perhaps be more aesthetically appealing, or easier to learn about or use. Truth is not the only important criterion. This is particular true of statistical truths, which may sometimes be so fuzzy as to be almost useless.
So, to recap, truth is best treated as a necessary illusion, often, but by no means always, necessary: it should not be taken too seriously outside the realm of statements about the comings and goings of everyday objects. The last sentence is itself close to asserting a truth whose validity it denies: a fully coherent argument here is not possible, but does this matter? Incoherence gives us more flexibility.