Interesting post, JH. Who is Robert Chapman, anyway? I have my doubts about that "But only 43 of them make up half of everything you say", too. Let me try and think, here--and of course this will have to discount proper nouns, as they would change from person to person. Here we go--as many as I can think of, of the words I use most commonly:
a, an, and, the, I, you, he, she, it, his, hers, yours, theirs, it's (apostrophe deliberate--I don't use "its" all that often), we, they, your, yours, be, am, is, are, were, was, go, going, to, for, some, too, went, gone, out, in, of, about, just, only, few, quite, think, thinking, thought, ask, asked, asking, read, reading, talk, talked, talking...
That's 51, and I haven't even gotten to the nouns yet. Did Mr. Chapman give a list of these 43?