It might be argued that certain mathematical statements are known without the corresponding proof. Consider the Gödel sentence invoked in the proof of Gödel's incompleteness theorem: the sentence is true, but it cannot be proved in the system under consideration (if the latter is consistent). Do we have knowledge of the Gödel sentence? Clearly we do, despite the fact that the sentence is not derivable in the system in question. As a result, the knowledge involved here is of a different sort than the one articulated in terms of what can be proved in a given system.