Well, duh. But really, he made up an astounding number of words and phrases! He lived in a time where language was flexing to accomodate the influences of merging dialects, and the populace had no expectation of a set syntax or vocabulary. Simply, the average audience member was prepared for verbal innovation due to the incredible linguistic commingling underway in 17thC london.
But Chaucer...now Chaucer had it good. He could choose between clawed and clew, ached and oke, climbed and clomb, and he variously used hi, hem and her to denote they, them and their. The English of the time had not yet settled into even a simple set of plurals, and gender was still applied slipshod across the land according to local dialect. Chaucer, a relatively cosmopolitan man, simply chose his verbiage according to scanning expediency. Lucky sod.
But all this is leading to my minor obsession; the greater and lesser vowel shifts that swept across the english language and changed vowel pronunciation forever. For example, the Domesday book is pronounced doomsday not because of some apocolyptic association with the census, but because "Dome" (for domestic census) was actually pronounced "doom" back in the day. Why did we lower the vowel sound? Nobody knows, and it happened to all vowels across the board. I'm fascinated by this, and if I have one complaint about Bill Bryson's fantastic book, "Mother Tongue", it's just that it can't unravel this particular knot for me. i guess i'll keep reading.