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← 03-03 Syntactic Structures

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

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