  In response to this question, most 20th century theorists followed  Chomsky in holding that language acquisition could not occur unless  much of the knowledge eventually attained were innate or inborn. The  gap between what speaker-hearers know about language (its grammar,  among other things) and the data they have access to during learning  (the pld) is just too broad to be bridged by any process of  learning alone. It follows that since children patently do learn  language, they are not linguistic ‘blank slates.’  Instead, Chomsky and his followers maintained, human children are  born knowing the ‘Universal Grammar’ or ‘UG,’ a theory describing the most fundamental properties of all natural  languages (e.g., the facts that elements leave traces behind when  they move, and that their movements are constrained in various ways). Learning a particular language thus becomes the comparatively simple  matter of elaborating upon this antecedently possessed knowledge, and hence appears a much more tractable task for young children to  attempt.