The 600,000 figure is way too low. The latest impossibly, impossible count I read about had the figure 200,000 times higher--and that article was from several years ago.

We have discussed here the impossibility of determining an accurate count of English vocabulary, especially so many very fine words never find their way into a dictionary, wonderful words such as my little pet 'google.'

But, for those who attempt to count professionally however they go about it, the count was over 800,000 several years back.

I, for one, think it would be fascinating to have a way of determining a person's personal vocabulary--including proper nouns. Seems one should get credit for all the persons, places, book titles, etc., one is familiar with.