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October 17

Antonym of conjunction "unless"

Wiktionary says "if". I say "even if". Who is correct?? Georgia guy (talk) 16:15, 17 October 2016 (UTC)[reply]

A unless B... vs. A if B vs. A even if B.

The "even if" sound clearer. Wiktionary is user input as Wikipedia is. Sourcing is important. Roget's might be a good resource. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:19, 17 October 2016 (UTC)[reply]

Oddly enough, neither Oxford online (British) nor Miriam-Webster Online (American) have unless as an option for their thesaurus. See [1] and [2]. Neither does the online Roget's Thesaurus: [3]. Sorry not to be of more help... Maybe the unabridged OED has it? I know a few people who patrol here have memberships. --Jayron 32 17:28, 17 October 2016 (UTC)[reply]

The big OED doesn't do antonyms, so its entry doesn't help except that one of the definitions is "if not" which suggests that the antonym is just "if". Perhaps the subtleties depend on usage. There is seldom such a thing as a perfect synonym or antonym. There is a technical discussion here. Dbfirs 17:45, 17 October 2016 (UTC)[reply]

In practice, it's often "provided". "The sun will not rise tomorrow unless the black dragon is slain." vs "The sun will rise tomorrow provided the black dragon is slain". --PalaceGuard008 (Talk) 17:55, 17 October 2016 (UTC)[reply]

Then there are "only if" and "if and only if" (the latter is beloved of logicians, who abbreviate it to iff). -- Jack of Oz ^{[pleasantries]} 19:53, 17 October 2016 (UTC)[reply]

Note that there is another possibility, that A will happen regardless of if B happens. Whether A happening unconditionally is the opposite of A being conditional on B is just a matter of opinion, though. StuRat (talk) 20:02, 17 October 2016 (UTC)[reply]

I've sometimes wondered what the difference between "only if" and "if and only if" ("iff") is. Isn't the latter a logically redundant version of the former? --Theurgist (talk) 00:00, 18 October 2016 (UTC)[reply]

Are you asking about English, or mathematical logic? In math logic, "A only if B" is exactly the same as "A implies B" (whereas "A if B" is exactly the same as "B implies A"). These terms have a purely truth functional interpretation (see material implication).

If you're asking about English, well, that's a lot more complicated. --Trovatore (talk) 00:29, 18 October 2016 (UTC)[reply]

Of course! Lulu is a poodle only if Lulu is a dog. (A → B) – that's true; Lulu is a poodle if and only if Lulu is a dog. (A ↔ B) – that's false. Lulu is a dog if Lulu is a poodle. (A ← B) – that's true as well. Silly me! --Theurgist (talk) 01:10, 18 October 2016 (UTC)[reply]