Knowledge and Doubt

Justified True Belief

For centuries, philosophers defined knowledge as justified true belief: you know something only if it is true, you believe it, and you have good reason for that belief. Descartes pushed this further by doubting everything he possibly could, searching for one belief that could not be shaken. He found it in the very act of thinking: even a deceived mind must exist to be deceived.

“I think, therefore I am.”

Where this sits in the course

“Knowledge and Doubt” is lesson 1 of 3 in What Can We Know?, a course about slow down on knowledge itself: doubt, experience, induction, and proof.. The lessons are sequenced rather than a menu, so this one assumes what came before it.

What Can We Know? is itself one of 18 courses in thinkr. The set opens with what philosophy is, moves through the Stoics and the Eastern traditions, then into what can be known, what exists, how to act and how power works — closing on practical reasoning you can use in an argument this week.

In the app this lesson is followed by 5 exercises that check whether the idea actually landed — and every answer, right or wrong, is explained rather than scored. That is the part a written page cannot reproduce.