After reading and rereading our stack of citations for the use of dichotomy, we have come to the conclusion that many people who use this word have only a general idea of what it means. This haziness on the part of the word’s users has resulted in a word whose meaning, aside from technical uses, is likewise hazy. For someone evaluating good and bad usage or even merely trying to describe usage accurately, dichotomy presents a ticklish problem.

Several usage commentators have responded to the uneasiness that dichotomy engenders by simply saying that it should not be used in general contexts to mean “division” or “split.” Frankly, we welcome such uses because they, at least, can be pinned down to a single, clear definition.

. . . the dichotomy between mind and body — Rollo May, Psychology Today, August 1969

This is actually sense 1 in both Webster’s Third and Merriam-Webster’s Collegiate Dictionary, and we find it entirely standard.

One usage commentator disapproves of using dichotomy “to mean anything divided into two or resulting from such a division; and thence to mean something paradoxical or ambivalent.” We certainly have evidence of dichotomy being used to mean “paradox” or some other vaguely similar meaning.

Herbert Hoover, a Quaker, fed milk to Belgian babies; Herbert Hoover as President of the United States had war veterans of the Bonus Army bombed out of Washington by tear gas. What is this profound dichotomy? — Alfred North Whitehead, Atlantic, March 1939

The amusing spectacle of the recent presidential vote in Florida should remind us of the persistence of the federal-state dichotomy — Eugene Genovese, Atlantic, March 2001

In our most recent analysis of this word, which appears in Merriam-Webster’s Collegiate Dictionary, Eleventh Edition, we define this sense as “something with seemingly contradictory qualities,” and we find it to be entirely standard.

However, in many cases of such dichotomizing, the message that gets across to the reader is chiefly that the writer is using a fancy, academic-sounding word. If this is the impression you want to convey, dichotomy will surely serve you. If you are mainly interested in having your sentence understood, however, you might be better off finding another way to word it.

From Merriam-Webster’s Concise Dictionary of English Usage.