Definition of Universal Grammar
It is a theory in linguistics that suggests that there are properties that all possible natural human languages have. It is credited to Noam Chomsky. It is an attempt to establish the properties and constraints common to all possible human languages. In other words, it is an innate system of principles underlying the human language faculty. This theory suggests that some rules of grammar are hard-wired into the brain, and manifest without being taught.*
A Universal Grammar, however, is not an account of the grammar of an individual language (e.g. English, or French). It is more precisely, a theory of grammar; it is, in Radford’s (1997:5) words, “a set of hypotheses about the nature of possible and impossible grammars of natural (i.e. human) languages”.
Principles and Parameters of UG
According to William Snyder and Diane Lillo-Martin, "the basic idea in PRINCIPLES AND PARAMETERS THEORY is to distinguish the invariants of human language (the principles) from the major points of cross-linguistic variation (the parameters )."
It asserts that knowledge of language relies on the structural relationship in the sentence rather than on the sequence of words.
The boy wrote a letter.
It breaks up into: (NP) the boy,(VP)wrote a letter(VP)further breaks into(V) wrote,(NP) a letter
149542526670000181927526670000328612524765000361950024765000 NP VP
1419225193675397192521844000314325022225004181475222250002152650222250 D N V NP
4495800181610039052501816100 The boy wrote D N...