Chaucer and Shakespeare are commonly cited milestones in the evolution of English, but the major change was far more compressed in time than 200 years. William Caxton:

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And certaynly our langage now used varyeth ferre from that which was used and spoken when I was borne.

He was born about 1422, a generation after Chaucer died.

All languages change, except dead ones. Perhaps the most well-known change in contemporary English is the meaning of the word gay.

[This message has been edited by yaktx (edited 01-18-2006).]