 Interrogative expressions can serve as the argument of certain clause-embedding predicates, as when someone is said to know, tell, care, or wonder who, what, whether, how, or why. Where the attitude predicate is knowledge, these sorts of examples are called cases of knowledge-wh. Knowledge-how in the sense of skill-possession, as in ‘Smith knows how to ride a bicycle’, has generated a literature of its own and is treated elsewhere (see the entry on  knowledge how).  