Before asking what we know, philosophy has to say where knowledge comes from. Empiricists ground it in experience — the outer senses together with the mind reflecting on its own operations — and deny any innate content; rationalists hold that reason — in some versions by way of innate ideas — reaches truths experience cannot supply. The dispute is not over which beliefs we happen to hold but over which source carries authority when experience and reason pull apart.
This is one of several questions once bundled together as "knowledge." A distinct question — whether space and time belong to things independently of human sensibility or are forms through which we experience them — is treated separately under Space, Time, and Experience, and how a belief becomes justified is a further question in its own right.