Is there a single definition of truth in philosophy?
Seeing multiple definitions has inclined me to believe that there is no proper definition of philosophy that everyone can agree on.
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welcome to PSE. The concept of truth is one of the head-spinners of philosophy.
Some philosophers believe that truth is a property possessed by all and only true propositions, statements, sentences, claims, &c. Just as a square has the property of being a figure in plane geometry with four equal angles, so a true statement has has the property of being true. The trouble is that while 'truth is a property possessed by all and only true propositions' tells us that truth is a property, it doesn't tell us what the property is. It comes down to no more than 'truth is truth', which I suppose we knew already.
There are theories about what the property is, e.g. 'correspondence with the facts'. Fine, except no-one has been able to say what a fact is without coming out with something like, 'a fact is what a true statement states'.
Deflationists deny that truth is a property of propositions, statements and the rest.
A deflationist is likely to offer some such formula as that :
'The proposition that-P is true if and only if p'
So the truth of the proposition that-P is true by virtue, not a a property of P but through an equivalence schema.
But this is a tricky area, and I must leave deflationists to speak for themselves and to argue their case more clearly than I can.
What I suggest is that truth is best regarded as a contrast concept or term. Wittgenstein said : don't look for the meaning, look for the use. In the present context this means, don't look for a single definition of 'truth' but consider how the word 'truth' is used in connection with propositions, statements, &c. 'Truth' contrasts with 'lie', 'accidental falsehood', 'misstatement', 'exaggeration', 'fiction', 'myth','fabrication' and many other concepts and terms. 'True' contrasts with 'inexact', 'inaccurate', 'inadequate' - the list could go on. Against these sets of oppositess neither 'truth' nor 'is true' has a single meaning. It has a contextual meaning in each case, and usually a clear one.
You will find different approaches on the site. I don't offer mine as the best. I do think, however, that my 'method of opposites'* will sometimes prove helpful in elucidiating how 'true' or 'is true' are used in ordinary language and in much technical language too. This is the bird in hand; there are plenty of birds in the bushes of theory and you should certainly seek them out.
*Actually Aristotle's : Nicomachean Ethics, Bk. V, 1:5-7, 1129a. Must tell the truth.
There are competing conceptions of truth: truth as correspondence to the world, as ideal utility, as coherence... As for all the most basic notions of philosophy, finding a consensual definition is not an easy task.
We can at least say that truth is a property of sentences (or of the propositions expressed by sentences) and that it has to do with their relation to the world.
It is widely recognised that there is a tight connection between truth and meaning, which can be captured in part by its disquotational property: the fact that the proposition "'F' is true" has the same content as the proposition "F" simpliciter. Minimalists/deflationists/pluralists about truth only recognise this property as what defines truth, which means, roughly, that saying that a sentence or proposition is true is just expressing one's commitment to assert it or to believe it. They'd think that any more substantial definition is doomed to fail.
Both previous answers tend to characterize truth as a correspondence between an idea and reality. Perhaps they lack two key ingredients, the first remarked by Descartes and Kierkegaard: truth is subjective. The second, truth depends on a subjective purpose.
If something is verifiable, truth can be said to be objective (e.g. the existence of the Higgs boson, the fact that earth is flat, the fact that smoking is bad).
But history has proven that the fact that something is verifiable does not mean that it is true. Philosophy of science is clear about that: science does not mean truth: science is just objective knowledge obtained using the scientific method. In consequence, we can say that not even scientific knowledge can be objectively true.
The problem is the level of objectivity to reach. Knowledge is a map of the territory, but it is not the territory. Moreover, each person has a map, and we can share points on the map. In addition, our representation of nature is extremely poor. The territory, nature, is pure energy (even matter is just energy), massive interactions, a reality in permanent change. Knowledge is like bad static pictures of a dynamic reality, representing tiny sections of the universe. The correspondence between both reality and objective knowledge (truth) would be impossible. In other words, there's no possibility for objectivity, only shared subjectivity. Several philosophers follow such perspective.
So, this would be a definition: truth is be the correspondence between reality and subjective knowledge. This fact add more relevance when we assess the history of knowledge and in particular, science. When we accepted the world was flat, or that Newton's laws were precise, or that the atom had only the behavior of a particle, we were just expressing our massive human-shared-subjectivity.
There's one more point about truth, which I didn't read about, but had discussions about (if someone provides a link, thanks in advance). Knowing truth has a purpose, which would be to determine behavior. In other words, truth has the purpose of knowing if something is good or bad: why do we search truth, in ultimate terms? Why do we think about it? Why do we make philosophy?
For example, why do we want to know if God exists? Why do we discuss whether the Barcelona is better than Real Madrid? Why do we argue about socialism or democrats? What is the truth lying behind such quest?
The answer seems to be survival. I argue about a political party in order to know if I should follow it and improve my probabilities of survival. I argue about a football team in order to get more supporters for my team in order to have a bigger group, which improves my probabilities of survival. I argue with my wife about the best detergent in order to improve the cleanness of glasses, to avoid getting sick and reduce my chances of survival. We learn quantum mechanics, not to write our findings on books, but to use the knowledge. Use it for what? To live better, that is, for improving our chances of survival.
So, truth is about the logical coherence between reality, knowledge and the subjective purpose of survival. It is natural to assume that any lack of coherence between this three aspects decrease our chances of survival. For example: for long time we've assumed that making money by cutting trees was a good thing to do. Reality was that cutting trees gave easy money. Subjective knowledge was coherent with such reality. But suddenly it turns to be negative: we've come to learn that cutting trees decrease our chances of survival. Now, we know that making money by cutting trees is really bad.
So, my personal definition, based on such philosophical ideas, and compatible with most other definitions would be this:
Truth is the coherence between reality, subjective knowledge and subjective purpose.
An example: at some point in our childhood, we start to take positions about what is true and what is false, following our instinct of survival. Scientists can state that eating lettuce is healthier than eating marshmallows, but that's not true for most children. Aren't children following their survival instincts? Well, they are. In fact it seems that eating vegetables is healthy for adults, but not for children, due to they could be vulnerable to the small amounts of toxins they carry. In addition, children can process sugar easily, which provides them of the energy kind they need. Truth is not only subjective, but must be coherent to a subjective purpose.
Update: just read sone reviews of 2018's Simon Blackburn's On Truth: he seems to address precisely the problem of the coherence of truth and purpose. But he would address it from a performative perspective (truth depends on the process of obtaining it). That looks inadequate to me: the natural consequence is the definition of two different domains of truth: scientific and ethical (ethics, morals, justice and most normative systems have the purpose of improving our survival). No need for that. It is enough to link truth with purpose.
The answer to your question is NO. And most philosophers would probably judge your following statement TRUE.
To understand the surprising confusion truth throws at us, consider the famous liar's paradox ("This sentence is false") and the question of whether a statement about a future event can be true. The latter ties in to determinism, which is itself very confusing and controversial.
Some have compared truth to a map. Maps aren't "true," of course; they're simply tools that help us navigate. Likewise, truth - or the search for truth, often expressed as theories in science - can be thought of as a useful guide, even if we can never know if it's the absolute truth.
Sam mentioned the Stanford Encyclopedia of Philosophy's article Truth. I would also recommend that you read some additional articles about truth, including accounts by the Internet Encyclopedia of Philosophy, Philosophy News and Encyclopedia Britannica.
It also helps to research some related terms, such as fact, theory, belief, falsehood, lie of omission, and many others, keeping in mind that some of these terms have very different definitions in or outside the philosophy arena.
It is completely trivial to define the notion of truth and we can all do it without having to rely on anything else but our own subjective experience.
For example, whenever I am in pain, I can truly say that I am in pain, and I will know that I am in pain and that therefore the statement "I am in pain" is true.
I won't need anything else to validate the notion of truth. And, presumably, we can all do that.
Of course, it just happens that I don't know whether it is true or not that the Earth is flat, but that in itself does not invalidate the notion of truth, it merely puts constraints on how we use it.
Truths about the material world are not inherently nonsensical, they are merely uncertain. Which is also why we have the twin notions of knowledge and belief.