  If that's the case, though, language mastery can be no simple matter. Modern linguistic theories have shown that human languages are vastly complex objects. The syntactic rules governing sentence formation and the semantic rules governing the assignment of meanings to sentences  and phrases are immensely complicated, yet language users apparently  apply them hundreds or thousands of times a day, quite effortlessly  and unconsciously. But if knowing a language is a matter of knowing  all these obscure rules, then acquiring a language emerges as the  monumental task of learning them all. Thus arose the  question that has driven much of modern linguistic theory: How could  mere children learn the myriad intricate rules that govern linguistic expression and comprehension in their language — and learn them solely from exposure to the language spoken around them?