Principles and parameters is a framework within generative linguistics in which the syntax of a natural language is described in accordance with general principles (i.e. abstract rules or grammars) and specific parameters (i.e. markers, switches) that for particular languages are either turned on or off. For example, the position of heads in phrases is determined by a parameter. Whether a language is head-initial or head-final is regarded as a parameter which is either on or off for particular languages (i.e. English is head-initial, whereas Japanese is head-final). Principles and parameters was largely formulated by the linguists Noam Chomsky and Howard Lasnik. Many linguists have worked within this framework, and for a period of time it was considered the dominant form of mainstream generative linguistics. Principles and parameters as a grammar framework is also known as government and binding theory. That is, the two terms principles and parameters and government and binding refer to the same school in the generative tradition of phrase structure grammars (as opposed to dependency grammars). However, Chomsky considers the term misleading. Framework The central idea of principles and parameters is that a person's syntactic knowledge can be modelled with two formal mechanisms: A finite set of fundamental principles that are common to all languages; e.g., that a sentence must always have a subject, even if it is not overtly pronounced. A finite set of parameters that determine syntactic variability amongst languages; e.g., a binary parameter that determines whether or not the subject of a sentence must be overtly pronounced (this example is sometimes referred to as the pro-drop parameter). Within this framework, the goal of linguistics is to identify all of the principles and parameters that are universal to human language (called universal grammar). As such, any attempt to explain the syntax of a particular language using a principle or parameter is cross-examined with the evidence available in other languages. This leads to continual refinement of the theoretical machinery of generative linguistics in an attempt to account for as much syntactic variation in human language as possible. Language acquisition The Principles and Parameters approach is a postulated solution to Plato's Problem, as defined and stipulated by Chomsky. This program seeks to explain the apparent gap between linguistic knowledge and linguistic competency. In particular, given finite and possibly incomplete input, how do children in different linguistic environments rapidly arrive at an accurate and complete grammar that seems