Comparison of Vocabulary Sizes in Different Eras

I was reading through one of Safire’s books lately, and was struck by how much of the contemporary vocabularly is of relatively recent origin (if typically derived ultimately from historic roots). At the same time, there are also a lot of archaic words which die out (or lose their historic meaning). Three questions:

[ol]
[li]How does the size of the English language compare to prior eras? I would have to assume that net-net it’s a lot bigger, and that it’s a lot easier for a new word to get created than for an old one to die out completely.[/li][li]How does the average person’s working vocabulary compare with that of a person in prior eras? My guess here is that it would also be somewhat bigger, but not by the same margin as the language as a whole (being more limited by the lack of necessesity and by mental capacity).[/li][li]If I’m correct on the first two of these, what’s the upper bound on how far the language as a whole or the vocabulary of an average person can expand?[/li][/ol]

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