What is the difference between epistemology and ontology?

Epistemology: what we can know

Ontology: what exists

(Often intertwined)

Expanding @Qingu‘s correct answer, I would say that “epistemology” is the study of knowledge and “ontology” is the study of existence.

It’s also important to mention that these are branches of philosophy.

Dictionary.com gives us this:

epistemology
a branch of philosophy that investigates the origin, nature, methods, and limits of human knowledge.

ontology
the branch of metaphysics that studies the nature of existence or being as such.

Episteme refers to knowledge, and ontos refers to being.

Much more comprehensive definitions can be found in many places, but those are the bare bones.

I’ll expand a bit on the previous answers which were excellent to give a couple of examples to make the concepts a bit less abstract. An example of an Ontological question in philosophy: “do numbers exist? if so what are they? where are they?” Answers might range from a “platonic heaven” of ideal concepts to only existing in the minds of people who happen to actually be thinking of a particular number at a specific moment in time.

An example of an epistemic question would be: “Are there certain fundamental first principles upon which all knowledge is built? If there are principles, how do we know they are true? What are they?”

@Jeruba Episteme = Ontos, as in having knowledge is being? I wonder….