UG refers to those grammatical properties thought to be shared by all (to be universal to all) derivations of human language (anything from Amharic to Zhuang). Per this conceptualization, UG is innate to all humans – people come "pre-wired" with this universal grammatical structure. A person's individual grammar (that which is unique to the person) develops from the interaction between the innate universal grammar and input from the environment, or primary linguistic data. This "analytic triplet" (McGilvray, ed., 2005, p. 51), UG + input = grammar, is the functional core of the theory. Language acquisition Several questions (or problems) motivate linguistic theorizing and investigation. Two such taken up in Chomskyan linguistics are the process of language acquisition in children, and "Plato's Problem". These subjects are interrelated and viewed as evidence in support of the theory of UG. One of the simplest ways to approach the concept of universal grammar is to pose a hypothetical question about an aspect of language acquisition in children – why does a child learn the language that it does. As a specific example, how can a child of Asian descent (say, born of Chinese parents) be set down in the middle of Topeka, Kansas and acquire "perfect English?" The answer is that the child does not start with "Chinese", or any other conventionally defined language, in its head. The child does start with general grammatical rules that determine linguistic properties. Children come equipped with universal grammar, from which any natural human language will develop – without instruction. All that is needed is passive input during the critical period—defined in linguistics as that period within which a child must have necessary and sufficient exposure to human language so that language acquisition occurs; without sufficient exposure to primary linguistic data, the UG does not have the necessary input for development of an individual grammar; this period is commonly recognized as spanning from birth to adolescence, generally up to the age of 12 years, though individual variations are possible. If what the child predominantly hears (or sees via sign) as it is maturing through this critical period is the English spoken in Topeka, Kansas, then that is what the child will acquire. This is why, regardless of a child's ethnic/racial background (or any other non-relevant factor, the child will know Cockney English, Egyptian Arabic, or isiZulu if the child's primary linguistic input is Cockney English, Egyptian Arabic, or