Truth is one of the key philosophical terms that has been discussed extensively and with great relevance for centuries. Theories about how truth can be determined are fundamental to this. Two of these theories are introduced in this article.
Adequacy conditions of truth
We all have a rough but good understanding of what can be called true. It should be clear to everyone that a fact that later turns out to be an error was never true. Many people think that the people of the Middle Ages knew that the sun orbited the earth, but in the end there was no truth in this pseudo-knowledge and therefore it was not knowledge from the beginning.
In order to speak of truth in an appropriate way and to be able to evaluate theories about truth according to an objective standard, special standards are required. These are also called adequacy conditions because they decide how appropriately a theory speaks about the concept of truth.
Adequacy conditions for theories define general conditions that every acceptable theory about a certain area must meet [1, p.39]. For us it will be sufficient if we observe the following criteria for truth [ Perhaps you will think about it for yourself: What do I mean by truth? ]:
(1) Truth is an absolute property: it cannot be that a person X has the belief that p, and another person Y also has the belief that p and that the belief of X is suddenly true, the belief but wrong from Y [ibid.].
(2) The truth value is in no way relative: truth is independent of persons, time and places. If something is true, then it is absolutely true, anytime, anywhere, for any person.
(3) Truth is not language-relative: The truth value of a sentence does not change because I express the sentence in different languages. Of course, the condition still applies here that one can even translate between languages.
About truth carriers
We’ve been talking about the truth all along, but do we even realize what can be true? Which thing is truth actually assigned to? – that is exactly what we have to clarify. The following three suggestions serve as a guide :
(a) Linguistic truth carriers: Your problem, however, is that truth should apply across languages.
- Sentences: Are an abstract linguistic form, e.g. “The earth is round.”
- Statements: Are specific verbal actions, eg “Do you know what time it is?”
(b) Psychic Truth Bearers: Your problem, however, is that truth should be objective and timeless.
- Judgments: Are concrete psychological events, e.g. holding true.
- Beliefs: Are concrete psychological states, e.g. opinions that are formed about the world.
(c) Abstract Truth Bearers: Your problem, unlike the others, lies in access.
- Proposition: Are abstract semantic objects that designate a true or false content of a sentence in a concrete context. In epistemology and thus now also with the topic of truth , it is basically only about propositions.
Two different schools of thought
If we now speak of the concrete theories of truth, there is classically a division into epistemic theories of truth and non-epistemic theories of truth (often also called realistic WT). The former says that truth can be defined by justification criteria [1, p.42]. In other words: S is true if and only if S is justified.
At first glance, this seems strange to us, above all because we have made the requirement for the criteria for truth that this should be an objective and absolute property. At first glance, on the other hand, the non-epistemic truth theories are more accessible to us, especially in the form of the correspondence theory. Let’s take a closer look at both of them.
Non-epistemic and epistemic theories are in conflict. These are their main sub-forms.
Epistemic Truth Theory: Coherence
A well-known representative of the epistemic theories of truth is the theory of coherence, which is to serve as an example here. The basis is that statements are truth carriers. As is well known, the term coherence means connection and it is precisely this mutual connection and agreement in relation to truthful statements that is capitalized in this theory.
In this way, statements can be accepted or rejected and are therefore considered true or false – this creates a system of statements. Just think of the sciences here: Newton’s axioms are true statements in physics. All other statements must now consistently exist with these, so that the system of physics is coherent.
The truth criterion of the coherence theory is therefore consistency between the already accepted statements of a system of statements that obviously have to support each other. Truth can therefore never fall to a single statement, but only to the entire system of statements.
The coherence theory: A belief is true if and only if it is an element in a coherent system of beliefs.
Problems of this epistemic theory of truth
Besides the fact that coherence theory ignores several of the criteria for truth, I would like to add three further criticisms here. As already said, coherence means on the one hand consistency and on the other hand a mutual justification of the statements of a system of statements.
The first point is fairly unproblematic because one can simply assume that there is no logical contradiction. Point number 2 poses a big problem: If I have to justify a statement P with a statement Q, don’t I already assume an understanding of truth?
If I do that (and it seems so) then this definition of truth is circular and therefore useless. Another point of criticism is a very plausible example: Let us assume that we are putting together a wonderfully logical and absolutely contradicting fairy tale. Is that the truth then?
Last but not least, it can be argued that the requirement that all statements are only truthful in relation to a system of statements is highly implausible and counter-intuitive. Why should a sentence like “I am in Stuttgart” only be true in relation to a system of statements?
Our intuitive understanding: correspondence theory
In addition to this rather modern theory of truth, there is also a downright classic that has not only been known for many centuries, but somehow appears in all of us as an intuitive understanding of truth. I am talking about correspondence theory, which says that something is true when it agrees with the world or with facts.
The correspondence theory: A proposition is true if and only if there is a fact with which it agrees.
That seems very obvious to all of us at first, doesn’t it? When I say “I’m in Stuttgart”, then this sentence is true when I’m in Stuttgart – sentence and fact match. This simple relation seems to be completely sufficient for our everyday life.
Of course, correspondence theory makes some assumptions, such as that there is some kind of outside world in which facts can take place. In addition, as a recognizer of these facts, I must have access to this outside world and assume that I am not deceived in it. Those are minor details.
Much more difficult is the requirement that there must be a match …
Problems of Correspondence Theory
Correspondence theory also has some problems, even if it is nowadays again one of the less problematic truth theories. Research over the past few decades has shown that non-epistemic theories in particular are on a rather shaky framework and have great weaknesses.
Correspondence theory gained momentum again on this path and is again comparatively good today. Nevertheless, its fundamental problems  cannot be brushed under the table. They are among others:
- Whatdoes what corresponds to?
- What is meant by agreementhere ?
The requirement for consensus is a difficult one. Do our thoughts match reality, or just beliefs match facts? How do they agree – is identity important here? There are a lot of things to question.
But there is a wonderful, very complicated solution that addresses all of these problems. The Polish-American mathematician and logician Alfred Tarski formulated the so-called T-Convention in a semantic truth theory that rehabilitated the concept of correspondence. 
More on this in another other (publication pending).