Showing Revision 1 created 05/04/2012 by Amara Bot.

1. Title:
   03-03 Syntactic Structures
2. Description:

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   Noam Chomsky is a philosopher and a linguist,
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   and in his seminal 1955 work "Syntactic Structures,"
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   he suggests that utterances have rules, syntactic rules,
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   and they're governed by formal grammars.
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   The problem with the wrote, wrote, wrote, de, de, de bag of words above
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   is that they don't form a grammatical sentence.
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   We much prefer grammatical sentences.
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    It's easier to interpret them and figure out what they mean.
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    We can write down these formal grammars
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    using a special notation.
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    Here these 5 lines together
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    are my formal grammar, and each one
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    is what is known as a rewrite rule.
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    The words that I've written in blue are called non-terminals.
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    If you have one of these things written in blue,
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    you can rewrite it with whatever is to the right of the arrow.
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    These words that I've written in black never occur on the left
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    of any one of our rewrite rules, so they can never be replaced.
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    Once you get there, you're stuck, and the process terminates.
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    We call them terminals.
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    Using these rules, if I start with sentence,
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    I can rewrite sentence to be subject verb,
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    and then I could rewrite that by picking any one of the rules
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    that has subject on the left.
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    Let's pick students.
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    I've only replaced subject, leaving this verb non-terminal alone.
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    But then I could replace verb with any one of these rules,
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    and at this point I think we're done.
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    The process terminates because I can't replace students or think
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    with anything, so here I've used 1, 2, 3, rewrite rules
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    to start from sentence and end up with a valid utterance.
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    This sort of maneuver with all these arrows is sometimes called
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    a derivation because I was able to derive
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    "students think" starting from sentence using these rewrite rules.
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    Even using this relatively simple grammar, however,
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    I have a few options.
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    Here I've shown another derivation starting with sentence.
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    Sentence goes to subject verb, verb goes to write,
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    subject goes to teachers, and I've produced another string
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    in the language of the grammar.
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    Both "students think" and also "teachers write"
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    can be produced by that grammar.