What is linguistics The publication of Chomsky s Syntactic Structures brought about a revolution in linguistics Prior to this work many linguists were concerned only with the description of languages Chomsky argues that a grammar cannot be identified with any list of sentences compiled by a linguist For example a linguist goes out in the field to study Navajo first hand and lists every sentence he obtains from his native speaker consultants Though he has been thorough and conscientious he will not have identified the set of grammatical sentences in Navajo and thus will not have determined its grammar This is because the grammar of Navajo should mirror the ability of the native speaker of that language to speak or understand an indefinite number of new sentences That is the grammar of Navajo or any language should mirror the knowledge of the speaker that enables him her to produce new sentences not heard or spoken before No list of sentences can do that since as soon as the list is complete there can be new sentences spoken which are not in the list Once again simple observation is not adequate to the task at hand In fact if the set of sentences for any language is infinite then simple observation no matter how long it lasts will not be adequate Instead a grammar must mirror the internal mechanism of the speaker hearer that will generate an infinite set of sentences Thus in the same way that the Copernican theory of planetary motion abstracts from simple observation to a theory that makes predictions about where the planets will be at some future time the grammar of a natural language must abstract from observed sentences to a theory of the internal mechanism of the speaker hearer to predict an infinite number of possible sentences in the language The woman is sleeping John thinks the woman is sleeping Harry believes John thinks the woman is sleeping Harry believes John thinks the woman in the picture is sleeping Etc For every sentence there is another sentence that is longer and includes it The list of sentences each one including the preceding one can go on indefinitely In a subsequent module we will look at a simple mechanism to produce these results For now consider the following model for the acquisition of the ability to speak and understand an infinite number of sentences Experience LAD Grammar In the model the LAD Language Acquisition Device is the internal mechanism that converts linguistic experience to knowledge of language The grammar output of this device is the internalized grammar in the mind of the speaker that can produce and understand an infinite number of sentences The experience that is input to the LAD is finite limited to the time frame of the experience