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Are these two words interchangeable? How do you know when to use one or the other?

For some sentences it is easy to know which one to use, but not for others. The type of sentences that are difficult are those that begin with "if" or "should."

Here's some example sentences:

  • Should you ever break up with your girlfriend, wouldn't you become lonely?
  • Should you lose this, won't finding another one be difficult?

Or any kind of sentence that is like "Should ___, wouldn't/won't ____?"

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won't = will not, wouldn't = would not. –  Kieren Johnstone Apr 11 '11 at 11:56
    
Yeah I know that. But there are some sentences where they seem to be interchangeable. –  language hacker Apr 11 '11 at 12:01
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Can you give an example please? –  Kieren Johnstone Apr 11 '11 at 12:01
    
Good example :) –  Kieren Johnstone Apr 11 '11 at 12:24
    
possible duplicate of Usage of "will" and "would" –  FumbleFingers Oct 17 '12 at 21:11
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6 Answers 6

up vote 12 down vote accepted

Contrary to what you seem to think, wouldn't and won't are almost never interchangeable.

The simple negative won't is used for future negative actions or for refusals.

  • I won't go to the store tomorrow if it's raining. (Future negative.)
  • I won't go to the dance with you. (Refusal.)

The negative wouldn't is used for counterfactual statements, and for future statements embedded in a past-tense narrative.

  • I wouldn't shout if I were you. (Counterfactual)
  • He said he wouldn't like it. (Future embedded in past narrative.)

In every case here, replacing won't with wouldn't results in something either ungrammatical, or it changes the meaning of the sentence.

Edit: An additional requirement for will/would is tense concord, which means that subordinate verbs in a complex or compound sentence must agree in tense with the main verbs. This applies to the two halves of an if/then construction, as well as to verbs in relative clauses. For this purpose, will is considered to be present tense, and would is past tense. So you see things like:

  • He will be dead if he goes to the store.
  • He would be dead if he went to the store.

  • He says he will open the envelope.

  • He said he would open the envelope.

In this case, the distinction between will/would doesn't carry any semantic weight, but is required by English grammar. Swapping will and would in any of the preceding sentences results in an ungrammatical utterance.

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What if the sentence begins with "if?" –  language hacker Apr 11 '11 at 12:19
    
@language, do you have a specific sentence in mind? Both the future negative example and the counterfactual example use if, and the words are not interchangeable there. –  JSBձոգչ Apr 11 '11 at 12:26
    
Here's an example sentence: "If you ever break up with your girlfriend, won't you become lonely?" It seems like "wouldn't" can also be used. –  language hacker Apr 11 '11 at 16:59
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@language: you can only use won't in that sentence. This is because English requires tense concord: both halves of a conditional must be in the same tense (though they may differ in aspect and mood). Since break up is in the present tense, the result clause must also be in the present tense, and for the purposes of tense concord will is considered present tense while would is considered past tense. Therefore, using won't in your example is correct, while using wouldn't is ungrammatical. –  JSBձոգչ Apr 11 '11 at 17:03
    
Then what about this: "Should you ever break up with your girlfriend, won't you become lonely?" Can "won't" be replaced with "wouldn't" in this sentence? –  language hacker Apr 11 '11 at 17:30
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As Colin mentions, in this context would implies a hypothetical situation, whereas will implies intention or (likely) prediction.

So to take one of the examples:

If* you ever break up with your girlfriend, won't you become lonely?

...implies a greater likelihood of the break-up occurring than:

If you ever break up with your girlfriend, wouldn't you become lonely?

In the latter case, because we are talking about a hypothetical occurrence, the first part of the sentence could well be changed to be subjunctive:

If you were to ever break up with your girlfriend, wouldn't you become lonely?

...in which case wouldn't has to be used instead of won't.

(* Note: I've used if rather than should here, as should sounds rather old-fashioned when used in this context, to my ears at least.)

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So if you use "were", then you have to use "wouldn't," but if you don't use "were," then you can use either "wouldn't" or "won't?" –  language hacker Apr 11 '11 at 16:58
    
Understanding the subjunctive tense is key here. +1. However, I think the second example isn't correct, as the first clause needs to be subjunctive "If you broke up" right alongside the consequence. –  Ben Voigt Apr 11 '11 at 23:45
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As Kieren has commented, won't is short for will not whereas wouldn't is short for would not. They're not interchangeable. e.g. you wouldn't write I won't do that if I were you, you'd write I wouldn't do that if I were you. If you're not going to be at a party you might write I won't be there and not I wouldn't be there.

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"Will" and its negative "won't" are about future intention or prediction.

"Would" and its negative "wouldn't" have a range of meanings, but the relevant one here is about hypothetical intention or prediction.

So "I won't go" is a statement of my actual intention.

"I wouldn't go" is saying something about my intention in some hypothetical situation.

I'm sure there are contexts when both can be used, but I think there will still be a difference in meaning.

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From Grammar in use — intermediate, 3rd Edition, pp. 40–41, Cambridge University Press, 2009:

You can use won't to say that somebody refuses to do something:

I've tried to give her advice, but she won't listen.

The car won't start. (=the car refuses to start)

Ibidem, pp. 68–69:

Somebody wouldn't do something = he/she refused to do it:

I tried to warn him, but he wouldn't listen to me. (= he refused to listen)

The car wouldn't start. (= it refused to start)

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Won't (Will [not]) versus Would

The question centers on the construct called "verb mood," three in English of which are: indicative (a matter of fact), imperative (a matter of necessity), subjunctive (a matter of possiblity). [See http://englishplus.com/grammar/00000347.htm, and links within.]

The mood "breakdown" (pun intended) for will:

  • Indicative: will
  • Imperative: shall, will (non-standard; contextually or with inflection)
  • Subjunctive: might, would

Wherever any mood form is shared (two or more forms appear together as a singular mood) those are interchangeable when intended meaning otherwise is not lost.

Here you see that won't (negation or will in Indicative or Imperative mood) never shares mood with would.

So the answer is, no.

If a thing would..., that is only a matter of possiblity, subject to doubt. If a thing will or shall..., neither is open to doubt.

(Will that answer your question? Or wouldn't it?)

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protected by RegDwigнt Aug 15 '12 at 13:01

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