I am having a hard time understanding the definition of dichotomy.

I saw this recent article from a Harvard student: "• Dichotomy means two mutually exclusive alternatives and does not mean difference or discrepancy. Correct: There is a dichotomy between even and odd numbers."

Does that support the Oxford Dictionary's definition?

"Division or contrast between two things that are or are represented as being opposed or entirely different:"

I'm just completely confused, now.

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  • The OED definition refers to a separation of something in 2 elements clearly opposed. But qualifying these 2 elements as "mutually exclusive" is not always appropriate in some usage of the word "dichotomy", for example in the "dichotomy between passion and reason". – Graffito Sep 17 '15 at 22:25
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    A dichotomy usually means (a) there are only two choices/possibilities and (b) they are mutually exclusive. Part (a) excludes the possibility of a third choice. Part (b) means that there are really two and not one, and that there is nothing that fits in both camps. – Drew Sep 17 '15 at 22:52

Dichotomy means cutting in two. What he says is true; his point seems to be that dichotomy is stronger than difference and discrepancy. (True, except: dichotomy is the cutting in two or strong difference between two ‘alternatives’; not the alternatives themselves.)


Aside from the meaning of "dichotomy" as the phase of the moon we call "half moon" and as a technical term of art in biology meaning a bifurcation, the original OED gives two definitions of the word. The first is any two-fold partition (i.e., there's one side, the other, and nothing in between) and the second is a two-fold division. As an example of the latter, the OED cites a source that contrasts the "popular" theological dichotomy of man into body and soul with the Christian trichotomy of body, soul, and spirit.

The supplement adds to the second definition "something paradoxical or ambivalent," and gives these examples:

By a dichotomy familiar to us all, a woman requires her own baby to be perfectly normal, and at the same time superior to all other babies.

Their uncritical use of the 'Communist' versus 'free world' dichotomy

The latter example serves to illustrate some of the sense of the charge of "false dichotomy," when you're asked to make a choice between two things that are presented (wrongly) as the only possible choices.

But if your knife is sharp enough to cleave a domain into two parts, then it makes sense that the parts be distinct in the criterion of the cut. Otherwise, you'd have no basis for making the incision in the first place.


The OED definition of dichotomy, as it relates to descriptive language, is given in two parts, below. (There are other specific senses of the word which relate to moon phases, and to botany/zoology)

However I do not believe it to be a word which demands precisely specific usage, and saying something is dichotomous, is a convenient way of pointing out that something divides into two parts, or two apparent parts. Personally, I would tend to employ it in any situation where, for example, I felt it necessary to illustrate that there were two ways of looking at something or an opposing argument. A close adjectival synonym to dichotomous, is polarised.

e.g. The spat between Nigel Dodds and John McDonnell in the House of Commons this week, reminded everyone in Britain of Northern Ireland's dichotomous religious history and their enduringly polarised society.

a. Division into two sharply defined or contrasting parts; (Logic) division into two mutually exclusive categories or genera; binary classification. Also: an instance of such division.

b. A sharp or paradoxical contrast resulting from such a division; something paradoxical, ambivalent, or contradictory.


I would like to keep it simple and break it down for you this way: two things, let's say answers to a question, are said to be mutually exclusive if there is no way they can be both true at the same time. For instance, a number can only be even or odd, not both at the same time, excluding a third possible answer. Dichotomy involves mutually exclusive alternatives or simply alternatives that are contradictory, opposed or strongly different. Examples for dichotomies not involving mutually exclusive options:

  • the dichotomy between reason and passion
  • The dichotomy between theory and practice

I hope it helps.

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