Updated: Dec 5, 2020
Empiricism is the doctrine that all knowledge is strictly observation based. This seems reasonable enough at first, but it suffers from a fatal defect.
Knowledge is knowledge of truths, not of objects. Observation apprises us of objects, not of truths about them.
Observation makes aware of rocks, trees, and birds. These are the things we observe.
We do not in any literal sense observe truths about these things.
Consequently, some non-empirical source of knowledge is needed to convert awareness of objects into awareness of truths