Self-evidence

In epistemology, which is the study of knowledge, a self-evident proposition is an idea that we know is true just by thinking about what it means. We don’t need proof or extra facts to understand it; our normal thinking can figure it out.

Some people who study knowledge say that nothing can be self-evident. But many believe that we can know some things are true just by thinking about them. For example, we know we are conscious and that we have free will. But we can’t say for sure about someone else’s thoughts or choices in the same way.

One example of a self-evident idea is: “A finite whole is greater than, or equal to, any of its parts.” This makes sense when we think about it, without needing more details or proof.

Analytic propositions

Some people say that a self-evident idea is one that cannot be untrue without confusing itself. Others say the same about an analytic proposition. However, these two ideas are not the same. An analytic proposition is not always self-evident.

If you understand and believe a self-evident idea, you don’t need proof for it. The same goes for knowing that saying the opposite would be confusing—you don’t need to prove that either. The confusion in self-evident ideas and analytic propositions works in different ways.

Not every analytic proposition is self-evident, and some think not all self-evident ideas are analytic. For example, knowing that you are aware and thinking is self-evident.

Other uses

In everyday conversations, when people say something is "self-evident," they usually just mean it's very clear. But in deeper thinking about knowledge, the idea is stricter.

Some important ideas about right and wrong may also feel clear and true without needing proof. For example, Alexander Hamilton mentioned ideas like "The means ought to be proportioned to the end" as clear truths in his writing called the Federalist No. 23. The United States Declaration of Independence famously says, "We hold these Truths to be self-evident, that all men are created equal..." Even though these ideas feel clear, some people debate if they truly need no proof.

In mathematics, a self-evident statement is one that doesn’t need a proof because it is clear on its own. Sometimes these are called axioms. Other statements prove themselves without extra help.