Preface: I question this here because the author is a full-time linguist.
Source: The semantics of "unless" by Brian Buccola BA (Classics, Mathematics) PhD (Linguistics)

Bonus question: If “unless” is semantically equivalent to logical “or”, then is the added inference associated with “unless”, which turns it into exclusive “or”, derived in the same way as the inference that, under normal circumstances, makes “or” be interpreted exclusively? Or is it just a coincidence that these two expressions, which both share a truth table with ∨ but differ in that one is a subordinator and the other a coordinator, both happen to be regularly strengthened into an exclusive interpretation?

Still trying to intuit 'unless', I pursue the answer to the question. My following example motivates me to conjecture that 'unless' means only the exclusive 'or'. Am I correct?

Suppose a rebellious child's refusal to drink anything forces his parents to admonish him:

  1. Unless you hydrate, you die.      Then:

⟺ 2. On a less or lower condition that you hydrate, you die.

⟺ 3. If you do not hydrate, you die.

⟹ 4. You hydrate orEXCLUSIVE you die.

In 4, I omit 'either' for brevity, and the 'or' must be interpreted exclusively; because if 'or' were interpreted inclusively, then 4 misrepresents the parent's Speech Act as informing the child of the conjunction (that humans can hydrate and die) which is a trivial fact (all hydrated humans are mortal and so must die).

  • This belongs at ELU.
    – curiousdannii
    Jan 20, 2016 at 23:51

2 Answers 2


Example #4 does NOT actually have an exclusive or. That would mean that it was impossible that you could both hydrate and die. #4 has the same truth table as #1 and #3, which contain a 'logical or' (~p v q) {watch out for ~~, since p = ~hydrate}. English 'or' is only exclusive when only one premise is possible: 'You hydrate or you don't hydrate.' or 'I saw a bird or a bat [which is a non-bird].'


It is not XOR as brought out above but logical inclusive OR as I suggest below.

Unless A -B.

Not (A) implies B.

Not(Not(A)) Or B.

A Or B

ie hydration Or Death.

Both can not be false ... It cant be that I don't hydrate and I don't die.

Ill love to see an example where Unless is strengthened to have an exclusive interpretation.

As per Oxford online; the word itself means except if.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.