Change is the only constant – antithesis or oxymoron?

Solution 1:

An antithesis is usually not stating the two things as equal in the same sentence and clause. It does not equate the two, it compares them. It would be considered an example of antithesis if it were written:

"Change is x." "Constancy is y."

However, an oxymoron, in its strict definition, requires that the two words be side by side, as in:

"X was undergoing constant change."

The phrase "The only constant is change..." (the original Asimov quote), or the phrase "Change is the only constant," is best described as a simple paradox.

Or, if you are feeling up to a literary debate with everyone and their grandmother, "irony."

Solution 2:

I wouldn't really call this an oxymoron, because that is usually considered to be a noun phrase instead of a statement. I would just call it a paradox, because it is a self-referential statement that produces an apparent semantic contradiction. But since it points to a truth by stating that contradiction it may simply be a form of irony. We immediately understand from your example that nothing is constant, even though at face value the statement would seem to indicate the exact opposite.

Similar statements:

All generalizations are false. [The statement is itself a generalization, yet it points to a truth.]

Nothing is impossible. [For that to be true, it would have to be possible for something to be impossible, yet it still underscores the opposite meaning.]