Logic.
There are nodes here that say: "logic goes against human nature"
"... people who are capable of thinking rationally..."
"Logic is concerned with the truth of statements about the world."
None of these statements is really true.
Logic is about creating rules and assumptions ('axioms') and following the rules to create new rules.
It's sort of like a game, you create the rules, and you follow them to see what happens ('derive').
Mathematics is a obviously a branch of logic. You start with defining numbers like 0,1,2,3 (Peano axioms) etc. and then work out where it leads you. But that's obvious.
Far less obviously, religion; contrary to most people's opinion, is also logical. You start with a concept of God and a few other assumptions and work out what happens as a result, what it tells you about life. But the question is whether it is true.
A good question is whether people are logical or not. I believe that, except for insane people, the bottom line is that human beings are inherently pretty logical- they follow rules, they essentially think. So, logic is what people do.
But that isn't really the issue. The real question is the one of truth.
So let's talk about truth. In logic truth has a technical meaning.
It means that something is derivable given the assumptions and the rules. You can prove it, given the axioms.
But most people use the word 'truth' quite differently. Most people use the word truth to mean 'axiom' or 'something I assume to correspond to reality'. That's quite different, but related.
So the real and far more interesting question is what is true, in the everyday sense of the word, so: is there a 'God', is there life after death, what does 'moral' mean; do they fancy me, do they care about me, is it good to eat, how do I get as much money as Bill Gates, what is life all about, would she slap me if I ask that, what is the truth?