If they want to get revenge, Abra, I don't mind.
But perhaps they don't.
They don't in that utterance is included in the verbal substitution do or ellipsis? Is the full form
They don't want to get revenge
If they want to get revenge, Abra, I don't mind.
But perhaps they don't.
They don't in that utterance is included in the verbal substitution do or ellipsis? Is the full form
They don't want to get revenge
Per Wikipedia, what you have is ellipsis: "words are omitted when the phrase needs to be repeated." The omitted words are "want to get revenge."
Substitution happens when a word is substituted for another word or words. That's not happening here. It would if your second sentence were "But perhaps they don't want that." In such a case, "that" would substitute for "to get revenge."
Notwant to get revenge; theNotrequires do-support for not: But perhaps they do not want to get revenge; do not contracts to don't: But perhaps they don't (want to get revenge); and finally, Conjunction Reduction deletes material identical with the first clause: But perhaps they don't. "Ellipsis" just means 'something is missing somewhere'; it's not a specific enough term for grammar. Context and conditions are important. – John Lawler Jul 12 '15 at 21:59