Years ago a friend told me about word pairs in which one word cannot exist without the other word. The example he used was inside and outside. That is, inside cannot exist without its necessary other half outside.

At the time he told me a name for these word pairs, which I have long forgotten. What is the name describing these word pairs?

  • 5
    Lots of words exist without their corresponding opposite. Consider portable: easily moved or carried. It doesn't have a ready, common antonym. There is no rule that a word needs to have an opposite to exist. A language could easily have "inside" and "not inside". Jul 15, 2015 at 21:06
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    I'm confused by @Mr.ShinyandNew安宇's comment and its upvotes - nowhere do I see the question assuming that all words come in pairs.
    – Alok
    Jul 15, 2015 at 21:50
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    @alok there are no words which cannot exist without an antonym. It's a false premise. Jul 15, 2015 at 22:16
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    @vladkornea words exist because we create them. Concepts can exist independently of the labels we assign them. You don't need the word "outside" to create the word "inside". Otherwise how would you even create "outside" to go with "inside"? "Prose" exists whether or not we have poetry. The label for it is only useful if we have done reason to distinguish prose from non-prose, but we don't need the word "poetry" for that. Jul 15, 2015 at 23:43
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    prose: written or spoken language in its ordinary form, without metrical structure. Jul 16, 2015 at 0:05

7 Answers 7


Consider complement

Either of two parts that complete the whole or mutually complete each other.

Similarly, counterpart

One of two parts that fit and complete each other.

both from American Heritage

  • adj. complementary used in Geometry to describe adjacent angles on a line.
    – Hugh
    Jul 15, 2015 at 21:39

Having two opposing concepts that are defined by each other is an example of yin yang duality which may be the word you're looking for.

Other than than, two words with opposite meanings are also antonyms or complementary to each other.


I think you are looking for binary opposition.

A binary opposition (also binary system) is a pair of related terms or concepts that are opposite in meaning. Binary opposition is the system by which, in language and thought, two theoretical opposites are strictly defined and set off against one another. It is the contrast between two mutually exclusive terms, such as on and off, up and down, left and right. Wikipedia

(emphasis mine)

Deconstruction theory touches upon binary oppositions and explains how one of them cannot exist without the other:

Deconstruction is interested in the hierarchic binaries set up within texts. These could be: man/woman, speech/writing, white/black, inside/outside, full/empty, identity/difference, light/dark, presence/absence, similarity/difference. In each of these binaries, one term is privileged over the other. A deconstructive reading would show how, even when a text appears to privilege one term over the other (say, inside over outside), the text's logic of rhetoric reveals that there can be no inside without the outside. In other words, deconstruction shows how the less privileged term is central to the dominant term. By showing this centrality deconstruction reverses the hierarchy, for if the inside can exist only if there is an outside it means that the outside is the dominant element.

In its next stage, deconstruction destabilizes this reverse hierarchy too. It questions the new hierarchy and thus leaves even the displaced one unstable. Thus, the text remains unresolvable where neither term is privileged - a situation called 'aporia'.

Contemporary Literary And Cultural Theory: From Structuralism To Ecocriticism by Nayar

(emphasis mine)

  • Unfortunately, this nonsense argument cannot explain why in some pairs of words in which one is clearly "privileged," the "hierarchy" remains "stable." Ruthless and ruthful, for example. The former is a common usage, and relies not on the existence of the latter, an archaic word most people are unaware of. Also, unfortunately, there are no operational definitions of "privileged," "centrality," "destabilizing," or "existence."
    – deadrat
    Jul 16, 2015 at 4:20
  • You didn't read it all. Sometimes none of them is privileged. Though it is more of a philosophical theory but influences the langugage. The actual answer is binary opposition.
    – ermanen
    Jul 16, 2015 at 4:32
  • I read it all. I think you mean that sometimes neither of them is privileged, but so what? That's not the case with my example. I have no objection to the term "binary opposition," just to the baggage that comes with it. In mathematics binary opposites (e.g., interior, exterior) are not mutually defined, so I doubt the fundamental philosophical insight.
    – deadrat
    Jul 16, 2015 at 4:58

Possibly Collocation, but those don't have to be together, they are just usually found going together when used in context.


Dichotomy is a good word. It implies a relationship to opposites or at least contrasting ideas. I'm Not sure if its what your looking for. Though, I do feel the question is rather vague.

  • As a first-time user, I appreciate the great contributions and discussions! As OP, the phrase "binary opposition" best fits my memory of my friends insight..The other offerings make for excellent 'ponderables' (yes, I made it up) and I appreciate all.
    – Art Bonney
    Jul 17, 2015 at 17:46

Inseparable gives more emphasis on the fact that something cannot exist alone.

Something can also be dependent upon something else.


Are you thinking of antonym? (dictionary.reference.com)

a word opposite in meaning to another. Fast is an antonym of slow.

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