In his 1949 book, The Concept of Mind, Gilbert Ryle describes two distinct species of knowledge: knowledge that and knowledge how. "Knowledge that" is also referred to as "propositional knowledge", presented in the form of sentences such as "S knows that G". Thus, where G represents the fact, "London is the capital of England", in knowing that G, S knows the fact "London is the capital of England". On the other hand, "knowing how to G" pertains to some action. Let us say that G equates to figure skating: specifically, performing a triple salchow (a jump). In saying "S knows how to G", one is not referring to facts about the salchow; rather, one is saying that S knows how to perform the manoeuvre.