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What is the word for words that are 'two sides of the same coin' as they are not always opposites... such as heads and tails.
Complement?
An example would be ball and strike in baseball. They are the only two possibilities for a pitch not hit. Are the contexts?
Tragedy and comedy but not positive and negative. Reading and writing and Peace and justice but not winning and losing.
It’s a bit unclear what you’re asking. But first, let’s make sure we’re understanding the idiom two sides of the same coin in the same way.
The OED’s entry for side n. offers:
c. With reference to a coin.
(a) two sides of the same coin and variants: two things, processes, etc., which are closely related or interdependent even though they seem different; two different aspects of the same situation or phenomenon.
Are you asking what the word is for a pair of words relative to the coin metaphor? They would indeed be — as you suggested — complements:
5. a. Something which, when added, completes or makes up a whole; each of two parts which mutually complete each other, or supply each other’s deficiencies.
We need both of the words or we don’t have two sides for our “coin.”
Situated metaphorically on either side of our coin, the words are now also opposites:
B. adj.
1. a. Situated on the other or further side, or on either side, of an intervening line, space, or thing; contrary in position; facing. Frequently with to and (now less commonly) from; formerly also with †against.
But maybe you are asking for a word that describes the semantic relationship between a particular pair of words?
Well, one might argue that they could all be cast as forms of opposites (if they couldn’t, we probably wouldn’t deploy them in a coin metaphor).
We have gradable antonyms — like laughter and tears — that sit on either end of a scale. They’re two sides of a human emotion coin.
We have binary antonyms — like winning and losing — where you have one or the other. They’re two sides of a game coin.
We have relational antonyms — like teacher and student — where you can’t be called a teacher if you don’t have a student and the other way around. They’re two sides of an education coin.
Ball and strike can be considered binary antonyms: pitches not hit must be one or the other. They’re two sides of the “not hit” coin. Same for fair and foul for pitches hit.
Reading is an act of intaking; writing is an opposite act — that of outputting. They’re two sides of a literacy coin.
And so on.
Definition sources: Oxford English Dictionary (login required)
I agree that complement works well in many cases. However, if you want to contrast two parts of some whole, or propose that two things can be thought of as complements, perhaps:
flip side
- an opposite, reverse, or sharply contrasted side or aspect of something or someone
The flip side of their charitable activities is a desire for publicity. Dictionary.com
The flip side of envy is, of course, idealisation. ref.
Greed is the flip side of envy. ref.
Now the flip side of envy is altruism. ref.
People-pleasing is the flip side of envy. ref.
Apropos the dialectic of religious consciousness, Aristophanic comedy offers another means of contemplating the flight of the Greek gods. As such, it is something of the flip side of the same phenomenon that tragedy reveals... Hegel on Tragedy and Comedy
The flip side of the celebration of freedom, though, is the challenge of order. ref.
This leads to grave injustice—the flip side of democracy—in the form of income concentration favoring a few and the deteriorating quality of life for the vast majority of citizens. ref.
