In epistemology, a causal theory of knowledge is one that states that in order for knowledge to exist, one must have a belief about something true, and that belief must have a causal relation with the truth.
For example, my knowledge that Socrates was a philosopher comes from the truth that Socrates as a philosopher, which led to Plato recording such details about Socrates, which in turn, led to others reprinting Plato’s works, and ultimately to me reading a work of Plato (or some derivation of one), and learning that Socrates was a philosopher. Similarly, my knowledge that there is beer in my glass is causally connected to my having poured beer into the glass, my having tasted the beer, and my state of mild intoxication.
The causal theory was first detailed by Alvin Goldman in a 1967 paper, “A Causal Theory of Knowing”. The intention of the causal theory is to solve the Gettier problem with the traditional definition of knowledge, that knowledge is justified true belief. Edmund Gettier provided two examples of justified true belief that one would not count as knowledge, both of which were the result of some inference that was made from a premise that was considered a justified belief, but not about something true.
The purpose of the causal theory is therefore to eliminate inferences that begin with a false proposition. A causal threory states that in order for there to be knowledge, there must be a causal chain, however complex, between the individual’s belief in some proposition, and the truth of the proposition itself.
Goldman specifically formulates the causal theory as follows:
S knows that p if and only if the fact p is causally connected in an “appropriate” way with S’ s believing p.¹
Goldman also suggests that S must be able to, at least in theory, correctly identify the causal connection between their belief and the truth in order for their belief to be knowledge. That is, S must not only know p but S must be able to recount how S knows p.
The causal theory of knowledge has, in its simplest form, also been challenged by Gettier-style examples in which the belief in question is indeed causally connected with the truth of the belief, but the individual holding the belief only holds it luckily.
Goldman himself presented such a counterexample (formulated by Carl Ginet) in a 1976 paper. His barn façades example supposes that one makes a direct empirical observation of an object and forms a belief about it, but is unaware of external factors that make the truth of that belief extraordinarily lucky.