The concept of truth is one of the most basic concepts in logic. There are certainly lots of controversies in philosophy about the nature of truth. However, for the purpose of critical thinking, we can adopt Aristotle’s definition:
To say of what is that it is not, or of what is not that it is, is false, while to say of what is that it is, and of what is not that it is not, is true. (Metaphysics, 1011b25)
The basic idea here is that truth is a matter of correspondence to reality. If you say “Paris is in France,” then your statement is true since Paris is indeed in France. Whereas “Paris is in Japan” is false since it is not the case. When a statement is true, logicians like to say that it has T (truth) as its truth-value. When a statement is false, its truth-value is F (falsehood). If a statement is neither true nor false, then we say it lacks a truth-value.
Aristotle’s simple definition does not imply we can always discover the truth. The sentence “Aristotle ate an odd number of olives during his life” is either true or false, but we would never know. Something can be objectively true even if nobody knows it or if people disagree about it. Objectivity is also quite compatible with changes in beliefs over time. People in the past used to think that the Earth is flat. But we no longer believe that. This change in perspective does not mean that truth is a matter of perspective.
Relativism is the view that there is no objective truth, that truth is ...