Epistemology

know-how knowledge

practical ability (“I know how to play guitar”

object knowledge

familiarity with an entity (“I know John”)

propositional knowledge

knowing a statement is true (“I know that 2+2=4”)

necessary condition

something MUST be true for something else to happen (If A is necessary for B, then if B is true, then A must be true)

sufficient condition

something GUARANTEES the outcome (if A is sufficient for B, if A is true, then B must be true)

justified true belief (JTB) theory 

to know something means three things must be true

1. belief

2. truth

3. justification

skepticism

doubting whether we can ever really satisfy all three necessary parts