Syntactic Structures
Chomsky described language as a generative system of rules and showed that grammaticality does not reduce to the probability of a word sequence.
Why it matters
Language processing followed rule-based parsing rather than probability estimation for thirty years.
The colourless green ideas example separates grammaticality from meaningfulness and from frequency. The book set out a programme in which a parser builds a tree from a formal grammar; systems such as STUDENT, ATN and LUNAR grew out of it. The return to statistics came only in the late 1980s.