20 Words to Watch

Supposedly, the following 20  words compose 25 percent of all spoken American English words:
Pronouns: I, you, they, it, he, she, what, that, this;
Articles: the, a; 
Verbs: is, have, do;
Prepositions: to, of, in, on;
Others: not, and.
They are often the words that trip up the best typists and proofreaders.