Philosophy
The Epistemology of A Priori Knowledge and Conceptual Truths
Quick fact
The classic example of a conceptual truth is 'All bachelors are unmarried'—it is true solely in virtue of the meanings of its terms, so we can know it without any empirical investigation, just by understanding the concepts involved.
Why this is interesting
You know that all bachelors are unmarried without ever meeting a bachelor. How can you be so sure of something you've never experienced?