- Are "depression" and "happiness" antonyms?
- Are they mutually exclusive?
- Does the absence of one imply the presence of the other?
(I am trying to ascertain the semantic validity of using depression-metrics as a gauge of happiness)
One could plausibly make the argument that both depression and happiness are emotions or moods or states of mind. For them to serve as antonyms they would need to operate on the same domain. Unfortunately, they are both nearly impossible to define without using other emotions, moods, states of mind as comparators. The idea of defining them as antonyms, for example, would be more useful when determining whether someone was depressed or happy. But a more typical antonym for happiness is sadness and the antonym for depression is elation.
As for the terms being mutually exclusive, they can be if (a) working within the same domain and (b) are being defined that way for the purpose of determining which one someone is. But they aren't necessarily so. Someone who is clinically depressed could feel a moment of happiness or vice versa.
But in no domain, shared or otherwise, would the absence of one imply the presence of the other. Someone who is entirely apathetic wouldn't feel either.
As for this goal, I recommend asking people in the fields of psychiatry and psychology instead of linguistics. We can tell you how people use the words; they can tell you about the actual moods and states of minds themselves. The odds are pretty good someone has an excellent answer to this intent but you aren't likely to find them here.
Not antonyms, no. For sure, a depressed person is unlikely to be happy, but one can be unhappy without being depressed.