I have found a restriction on the use of "unless" which was difficult to explain to my students (advanced ESL).

The student's sentence was:

I would have had to go to the bank unless you had lent me the money.

Several others produced similar sentences. How can we explain the difference in acceptability between:

  • They'll kill her unless she gives them the money.

  • *They would have killed her unless she gave them the money.

  • They wouldn't have robbed her unless they were really poor.
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    The student's sentence is confusing because one might go to the bank if one gets the money (to put it in the bank) or if one doesn't get the money (to try to borrow money from the bank). But, assuming it's the latter, normally one would expect to see "I would not have had to go to the bank if you had lent me the money." or "I will have to go to the bank unless you lend me the money" – Max Williams Jun 7 '16 at 10:11
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    Or (to follow OP's wording more closely) "I would have had to go to the bank if you hadn't lent me the money." Just an 'of the top of my head' thought: is "unless" more commonly used in a future sense than when referring to past events? – TrevorD Jun 7 '16 at 10:38
  • I'm not going to try to explain the syntactic differences, but the use of unless in the way you describe is typical of an illiterate rural US vernacular. – Hot Licks Jun 7 '16 at 11:44
  • Their sentence looks perfectly fine to me. Shrugs. – Araucaria Jun 7 '16 at 12:40

I think these are forms of the restriction described rather laconically by Cambridge Dictionaries Online as "We don’t use unless for impossible conditions". I would say it as "only use 'unless' for a condition where you know whether or not it obtains".

So it works in the future, and your third example shows that it works in the past when the condition is an unknown; but not in the common case when we are talking hypotheticals but we actually know what happened: then we can only use "if ... not".

  • Thanks. That was my feeling about it too but I wanted someone to confirm it! – Michael Heyman Jun 11 '16 at 0:24

In the grammatical cases, "unless (S)" is equivalent to "if (not (S))". In the ungrammatical cases, instead, the supposed equivalence would have to be to "if (perfect (not (S)))". That is, the problem is that "not" is not in the immediate scope of "if", because perfect "have" intervenes between "if" and "not".

  • Thanks for your answer. I'm afraid I'm only a lowly language centre teacher, not a linguist, and I don't fully understand it. Can you recommend a textbook that explains this type of analysis? Thanks. – Michael Heyman Jun 11 '16 at 0:23
  • McCawley's The Syntactic Phenomena of English is very good. I just looked for discussion of "if not"="unless" in this and found that McCawley does not agree with what I said. It's here: books.google.com/… – Greg Lee Jun 11 '16 at 4:07

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