Regarding the use of unless in a remote conditional*, The Cambridge Grammar (p755) says:

Unless occurs in open conditionals and, less freely, remote ones:



iv I wouldn't suggest such a plan unless I thought it was feasible.


The implicature of the remote version, as in [iv], is that not-P is false or probably false: [iv] conveys that I do think it is feasible.

Although The Cambridge Grammar says unless "occurs less freely in a remote conditional" than in an open conditional, [52iv] is the only example in the Cambridge Grammar of unless being used in a remote conditional. Therefore, the book fails to address the limitations of unless occurring in remote conditionals.

What are the limitations?

For example, does this work?

I wouldn't have suggested such a plan unless I had thought it was feasible.

For those who are not familiar with the Cambridge Grammar terminology, a remote conditional is explained as follows:

The remote construction differs from the open in that it entertains the condition as being satisfied in a world which is potentially different from the actual world.

And the remote conditional corresponds to the second and third conditionals in traditional grammar.


The question specifically asks about the validity of

I wouldn't have suggested such a plan unless I had thought it was feasible.

As the title suggests, however, what I'm looking for is a more general answer detailing the limitations of 'unless' in remote conditionals as only vaguely suggested by the Cambridge Grammar, than simply discussing the validity of the given example sentence.

So please don't be limited by the example sentence and feel free to add other example sentences to better answer the question, as you see fit.

  • Apparently the "if-clause" (negated to an "unless-clause" in your example) is called the protasis, and according to that link, and the "main" clause is the apodosis. Someone in that discussion says If the verb refers to future time, the present is used in the protasis, otherwise the tense is not changed, and the verb in the protasis is in the same tense as it would be in a normal statement. Commented Aug 29, 2018 at 15:18
  • ...he continues... In the remote conditional, the preterite (simple past form) is used in the protasis , and the "would" form (or similar, e.g. "could") is used in the main clause (apodosis). The remote conditional is used in (at least) two different circumstances: 1) a condition referring to the present that is believed to be counterfactual, e.g. a feminist atheist might say If God existed she would be omnipotent. 2) a hypothetical future condition that does not seem likely: If they won this match they would get into the next round. If that helps. Commented Aug 29, 2018 at 15:20
  • Using Past Perfect for the protasis in your example I wouldn't have suggested such a plan unless I had thought it was feasible pragmatically implies that you did think it was feasible back when you made the suggestion, but you no longer think that now. Commented Aug 29, 2018 at 15:35
  • Why should it discuss the limitations?
    – Xanne
    Commented Aug 29, 2018 at 18:46
  • @FumbleFingers So do you find I wouldn't have suggested such a plan unless I had thought it was feasible to be natural English?
    – JK2
    Commented Aug 30, 2018 at 2:07

2 Answers 2


Your sentence sounds ok to me, but I can think of others that don't.

e.g. incorrect: *Unless he had died, he would have finished writing his book.
(correct: If he hadn't died, he would have finished writing his book.)

The results of the first few google hits were contradictory.

Cambridge Dictionary


We don’t use unless for impossible conditions:

If the government had not raised food prices, there would not have been so many protests.

Not: *Unless the government had raised food prices …

I agree on their sample sentence being incorrect, but their rule would imply that your sample sentence was incorrect too.

On the other hand English language resources gives several examples of unless with the remote (impossible) conditionals.

Our director would not have signed the contract if she hadn't had a lawyer present.
Our director would not have signed the contract unless she had had a lawyer present.

I wouldn't have phoned him if you hadn't suggested it.
I wouldn't have phoned him unless you'd suggested it.

They would have shot her if she hadn't given them the money. They would have shot her unless she'd given them the money.

I assume Cambridge Dictionary would have rejected these. The examples without 'unless' do sound better stylistically imo; perhaps it's a case of where the authority draws their line; I'm not sure.

But there is another problem more general than the use of unless with remote conditionals.

From Micheal Swan, Practical English Usage, second edition, p.602:

When unless cannot be used

Unless (=except if) can be used instead of if not when we refer to exceptional circumstances which would change a situation. We do not use unless to refer to something negative that would be the main cause of the situation that we are talking about.

This seems to work in your example:

I wouldn't have suggested such a plan if I hadn't thought it was feasible

can be rewritten

I wouldn't have suggested such a plan unless (except if) I had thought it was feasible.

It also seems to explain why you can write:

If he hadn't died, he would have finished writing his book

but you can't write the first example I gave:

(incorrect)*Unless he had died, he would have finished the book.

The main cause of him not finishing his book is dying. Unless here doesn't mean except if.

So overall it seems 1) a case of where to draw the line; some grammars find using unless for the 'impossible conditional' generally inacceptable; more accept it. 2) In cases where 'unless' would refer to something negative that is the main cause, it can't be used.


Note: The discussion and the contradictory grammar sources make me think that there are borderline cases with some 'unless' structures, and the judgement on how acceptable or unacceptable it is to use these may depend upon how prescriptive or descriptive a grammar is. On the ELL site, I found what I thought was a good explanation on the nuances of 'unless', which specifically considered an example from Micheal Swan (Araucaria's answer).

  • My take on Swan's test is such that "the situation that we are talking about", as Swan put it, is his finishing writing the book, rather than his dying. If so, the test is whether his not dying is the main cause of his finishing writing the book, which it isn't. Therefore, if anything, the last sentence is not banned by Swan's test. No?
    – JK2
    Commented Sep 4, 2018 at 16:31
  • Can I assume that the sentence sounds wrong to you? For me, it clearly does not sound English. But we understand the Swan explanation completely differently. In the sample sentence his dying is the main cause for not finishing the book. This is why, according to Swan's reasoning, you cannot subsitute 'unless' for 'if (he had) not (died)'
    – S Conroy
    Commented Sep 4, 2018 at 22:22
  • P.S. I'm not sure exactly if I understood your understanding... In any case, to be clear, in the sentence where the 'unless' clause is to substitute for the 'if' clause (if he hadn't died he would have finished the book) the implication is that he did die.
    – S Conroy
    Commented Sep 4, 2018 at 22:42
  • As far as I know Micheal Swan is the author of 'Practical English Usage', not 'English Grammar in Use'. So I guess you meant PEU. I don't know which edition you've cited, but I've got the third edition of PEU. There, Swan says this: Unless is not used when the meaning is more like 'because...not'. My wife will be angry if I'm not home by 7.00 (NOT My wife will be angry unless I get home by 7.00 - She will be angry because I'm not home.)
    – JK2
    Commented Sep 5, 2018 at 1:35
  • So Swan checks if you can replace 'if...not' with 'because...not'. If we apply this to your last example, we should be checking whether his not dying is the main cause of his finishing writing the book, which it isn't. But I'm afraid you were doing the test the other way around.
    – JK2
    Commented Sep 5, 2018 at 1:42

From 1896 to 1902, the Free Church Scottish theologian Alexander Whyte published a six-volume work, apparently based on homilies, describing important biblical characters:

Unless he [Moses] had had it in him, vice or virtue, to strike that bold blow at that insolent Egyptian [Ex 2.11–15], he would never have had it in him to strike off Israel’s fetters. If he had hesitated and calculated and looked this way and that way that day, we would not have had his perfected meekness before us for our text tonight [Num 12.3].— Alexander Whyte, Bible Characters, 2011 (orig.1896–1902).

enter image description here

Dalziel’s Bible Gallery, 1880, Plate 25. Scan: Simon Cooke.

The second sentence is a standard past closed conditional musing that had Moses hesitated rather than taken immediate action, the Exodus saga would never have been told. Yet Moses did act, and thus Whyte’s congregation and readers may contemplate Moses as an exemplar of “perfected meekness,” i.e., humility. Both clauses in a past closed conditional are contrary to fact, hypothesizing about a condition and result that might have happened but didn’t.

The first sentence, with the introductory unless clause, employs the same pairing of tenses as the second: past tense subjunctive (indistinquishable in English from the pluperfect) and past conditional mood with “would have.” While the result clause is contrafactual, the unless-clause is, in terms of the biblical narrative, true: Moses indeed “had it in him” to murder the oppressive Egyptian overseer; thus he also “had it in him” to lead the Hebrews to freedom.

The limits placed on unless in remote conditionals are thus ultimately semantic: because of the not inherent to the conjunction itself, either the protasis (unless-clause) or the apodosis (result/consequence clause) may be contrafactual, but never both at once.

This is most obvious in a sentence with unless which is not a true conditional, but states a law of nature:

Many types of fruit trees, including some apples, pears, plums and sweet cherries, will not produce fruit unless they are pollinated. — James Dwyer, John Albert, ”Dwarf fruit trees: big producers in tiny plots,” Popular Mechanics v. 147, 4 (Apr. 1977), 94.

Of the statements “no fruit” and “pollination,” only one can be true.

The Remote Exception

Although academic discourse has concentrated mostly on conditionals such as Whyte’s —and whether they are even grammatical — there are other instances of contrafactual unless worth exploring, especially since they can be rather fun.

When an unless clause is immediately recognized as contrafactual, not only is the apodosis valid or true, but the more absurd or humorous the unreal protasis, the more the apodosis is affirmed:

The seaweed salad couldn’t have been any better unless it had been brought to me by a hot naked dude. — Vegan Coach, Review of Beyond Sushi (restaurant, NYC), 6 June 2016.

She appeared to make a deliberate effort to downplay her beauty, which was impossible unless she wore a sheet that covered her from head to toe. — Sherral D. Kahey Without Probation, Parole, or Suspension of Sentence, 2012.

Unless she had flown there on wings, he could not see how Frankie could possibly have got to the Anglers’ Arms ahead of him … — Agatha Christie, Why Didn’t They Ask Evans?, 1934.

My mother normally wouldn’t have called me at that hour unless a tornado had moved through her apartment. “Gerry, I need you to come over and help me. I'm not feeling so good,” she said, and this time I believed her. — Geraldine Ferraro, Framing a Life: A Family Memoir, 1998, 172.

This construction also works in the present tense, though for this writer not as successfully:

Additionally LeBron's signature skill is probably his otherworldly passing ability, which of course would not help him in a game of one-on-one unless he were allowed to clone himself and have it still technically count as “one-on-one” because his teammate is also LeBron James. — Jack Moore, “Could Michael Jordan Beat LeBron James in One-On-One?” GQ website, 10 Aug. 2015.

Hyperbole, clones, and nude waitstaff aside, an unless clause always sets up a simple binary where either the protasis or apodosis is true or will/would occur, but never both at the same time. If the condition imposed by unless is patently absurd, the conclusion is obvious. Even a small step into the realm of the possible, however, creates enough ambiguity that a conditional must be regarded as open.

Unless they had found their way to this bank and found a place to hang on, they were dead. The stillness was so heavy he felt sure they were not alive. — Mildred Walker, Unless the Wind Turns, 1996, 220.

Are they dead or did they manage to reach the riverbank and survive? Only one of these possibilities can be true. Read further to find out which!

The Open Exception

Remote may not be the best choice of descriptors for conditionals, because if there is a possibility, however remote, that either the protasis or apodosis may be true or later revealed as such, then the conditional is not remote, but open:

If James were to die, for instance, or if he were to transfer his affections, Buckingham might well be left homeless. He would also have very little to live on, unless he had managed, during his years in favour … to accumulate capital. — Roger Lockyer, Buckingham: The Life and Political Career of George Villiers, 2014.

She saw herself hating her husband, and she knew that, unless she were careful, she would smash her form of life and bring catastrophe upon him and upon herself. So in very fear, she went quiet. — D. H. Lawrence, “Daughters of the Vicar,” Selected Short Stories, 2012. Originally in The Prussian Officer and Other Stories, London, 1914.

In the Lawrence short story, the ambiguity lasts only until the next sentence, but it is still an open conditional. Given that liquid assets and frugality were generally in short supply among the Jacobean aristocracy, the chances that the first Earl of Buckingham had much cash before his assassination are slim, but still within the realm of possibility, thus open.

Unless in Contrafactual Conditionals

Acknowledging that numerous grammarians — Quirk et al., Longman’s, Geis, Bollinger, etc. — consider contrafactual unless ungrammatical, the Japanese scholar Takao Fujita maintains in a short article that this unusual outburst of proscriptivism in the 1970s and 80s lacks basis in actual usage. The usual method of demonstrating that contrafactual unless is ungrammatical, i.e., minimal pairs where unless produces nonsense while the if…not counterpart is unobjectionable, should not be the deciding factor, Fujita says, when there are reputable authors who use this construction.

To judge by what little is available online concerning the topic, however, contrafactual unless seems to be acceptable in well-formed sentences, and the earlier discourse has apparently died down, one reason why CSEL, which otherwise takes great pleasure in debunking baseless proscriptivism, doesn’t mention it.

The problem I have with the whole question is the dissonance between grammatical form and actual content. With an exclusive focus on grammar, the rhetorical strategy behind this construction, so similar to a standard third conditional, is ignored: the unless protasis, though half of a speculative or hypothetical proposition, is not actually contrafactual, but assumed true, thus affirming strongly the opposite of the apodosis, which is really the whole point of the utterance. In this construction, unless dons the guise of being contrary to fact, while the rhetorical strategy of the construction is just the opposite. It’s not the naked waiter with the seaweed salad, but it is Moses having “it in him.”

We should not have asserted in our last number that Benefit Societies were very ill calculated to secure the comfort and independence of the workman, unless we had had something better to offer to their notice. — The Co-operator No. 13, 1 May 1829.

The unless clause is assumed to be true, thus the editors indeed asserted the disadvantages of benefit societies. The apodosis is false, but the point is its unspoken affirmative twin. Other examples follow the same pattern: an apodosis cast as a negative of a current state of affairs is proven false by an unless clause whose assumed truth is essential to the sentence.

Hesiod would not have recorded this relationship, unless he had believed, probably in the seventh century, that the Macedones were a Greek speaking people. — Nicholas G. L. Hammond, The Macedonian State, 1989.

But we must never forget that we would not have made the progress toward lasting peace that we have made in this past year unless we had had the military strength that commanded respect. — Richard Nixon, “Address to the Nation About Vietnam and Domestic Problems,” 29 Mar. 1973.

I am quite satisfied that the defendant would not have told Mr. Appelby about the rumour unless he had obtained his information from some source which he considered to be reliable. — Ngope v. O’Brien Quinn, 1987, Botswana e-Laws [broken link].

”I was so lonely — you know, you must have read that story I wrote; you couldn’t have painted that picture unless you had, and unless you had understood.” — Agatha Christie, “The Lonely God,” first pub. Royal Magazine, London, 1926.

“I believe Semyonov was not a merchant navy deckhand, but a courier. That conclusion seems to me unavoidable. I do not believe he would have gone to those lengths to protect what he was carrying, or to end his life to avoid what he must have thought would be interrogation by us, unless he had been instructed his mission was of crucial importance.” — Frederick Forsyth, The Fourth Protocol, Part 3, ch. 16, 1984.

It is not surprising that writers such as Frederick Forsyth and Agatha Christie using this construction — Fujita adduces an example from another work — beacause for them, it is less rhetoric than deductive reasoning, in these last two sentences beginning with a positive statement about a current state, then speculating how one got there.


The limitations on unless in closed conditionals is inherent in the meaning and semantic function of the word: a binary structure where only one, but not both propositions in a conditional sentence may be contrary to fact. This means statistically, unless will occur more frequently in open conditionals and “less freely” in closed ones.

  • I appreciate your research effort. That said, since my question is based on CGEL and your conclusion is also trying to answer CGEL's proposition "Unless occurs in open conditionals and, less freely, remote ones", I think I should be pointing out that the terminology 'open/remote conditional' used in CGEL is quite different from your own. In your first sentence having Unless he [Moses] had had it in him, for instance, CGEL would call that sentence 'a remote conditional' regardless of whether Moses actually had it in him in the real world, which he did.
    – JK2
    Commented Sep 10, 2018 at 3:47
  • Therefore, CGEL refrains from using the terminology 'counterfactual conditional' because you could have a remote conditional ending up describing the actual world.
    – JK2
    Commented Sep 10, 2018 at 3:49
  • But +1 for the research effort and also citing the interesting paper on unless.
    – JK2
    Commented Sep 10, 2018 at 4:29
  • You cited: The remote construction differs from the open in that it entertains the condition as being satisfied in a world which is potentially different from the actual world. Since the true unless-clauses are very much part of the actual world, but the false ones like people flying or being served by nude waiters very much aren't, then the later are remote but the true ones are something else. Either that, or this definition is inadequate.
    – KarlG
    Commented Sep 10, 2018 at 7:09
  • The key word of that definition is potentially, meaning that even a remote conditional can describe the actual world or a hypothetical world, depending on context.
    – JK2
    Commented Sep 10, 2018 at 7:53

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