Conditional Sentences

Some conditional clauses beginning with if suggest that a situation is real - that is, the situation is or was true, or may have been or may become true:

• If anyone phones, tell them I'll be back at 11.00.

• If you really want to learn Italian, you need to spend some time in Italy.

Others suggest that a situation is unreal - that is, the situation is imaginary or untrue:

• What would you do if you won the lottery?

• If you had started out earlier, you wouldn't have been so late.

Compare: • If I go to Berlin, I'll travel by train. (= real conditional) and • If I went to Berlin, I'd travel by train. (= unreal conditional)

In the first, the speaker is thinking of going to Berlin (it is a real future possibility), but in the second, the speaker is not thinking of doing so. The second might be giving someone advice.  In real conditionals we use tenses as in other kinds of sentences: we use present tenses to talk about the present or unchanging relationships, and past tenses to talk about the past:

• If you leave now, you'll be home in two hours.

• If I made the wrong decision then I apologize.

• If water is frozen, it expands.

However, when we talk about the future, we use a present tense, not will:

• I'll give you a lift if it rains, (not ...if it will rain...)

In unreal conditionals, to talk about present or future situations, we use a past tense (either simple or continuous) in the if-clause and would + bare infinitive in the main clause:

• If my grandfather was/were still alive, he would be a hundred today.

• If you were driving from London to Glasgow, which way would you go?

• I'd (=would) offer to give you a lift if I had my car here.

Notice that we sometimes use if...were instead of if...was. When we talk about something that might have happened in the past, but didn't, then we use if + past perfect and would have + past participle in the main clause:

• If I had known how difficult the job was, I wouldn't have taken it. 

• If she hadn't been ill, she would have gone to the concert. 

In unreal conditionals, we can also use could/might/should (have) instead of would (have):

• If I lived out of town, I could take up gardening.

• They might have found a better hotel if they had driven a few more kilometers.

In some unreal conditionals we use mixed tenses. That is, a past tense in the if-clause and would have + past participle in the main clause, or a past perfect in the if-clause and would + bare infinitive in the main clause: 

• If Bob wasn't so lazy, he would have passed the exam easily.

• If the doctor had been called earlier, she would still be alive today.

Notice that in unreal conditional sentences: • we don't use the past simple or past perfect in the main clause:

• If we were serious about pollution, we would spend more money on research, (not ...we spent... or ...we had spent...).

• we don't use would in an if-clause:

• If I had a more reliable car, I'd drive to Spain rather than fly. (not If I would have...) 
 
In unreal conditionals we use if...were + to-infinitive to talk about imaginary future situations:

• If the technology were to become available, we would be able to expand the business.

• If he were to have a chance of success, he would need to move to London.

However, notice that we can't use this pattern with many verbs that describe a state, including know, like, remember, understand:

• If I knew they were honest, I'd gladly lend them the money, (not If I were to know...)

We sometimes use this pattern to make a suggestion sound more polite:

• If you were to move over, we could all sit on the sofa.

If the first verb in a conditional if-clause is should, were, or had we can leave out if and put the verb at the start of the clause. We do this particularly in formal or literary English:

• Should any of this cost you anything, send me the bill. (= If any of this should cost...)

• It would be embarrassing, were she to find out the truth. (= ...if she were to find out...)

• Had they not rushed Dan to hospital, he would have died. (= If they hadn't rushed Dan...)

We use if it was/were not for + noun to say that one situation is dependent on another situation or on a person. When we talk about the past we use If it had not been for + noun:

• If it wasn't/weren't for Vivian, the conference  wouldn't be going ahead.

• If it hadn't been for my parents, I would never have gone to university.

In formal and literary language, we can also use Were it not for... and Had it not been for...: • Were it not for Vivian... • Had it not been for my parents... We often use but for + noun with a similar meaning:

• But for Jim's support, I wouldn't have got the job. (= If it hadn't been for Jim...)

We don't usually use if...will in conditional sentences. However, we can use if...will when we talk about a result of something in the main clause.

Compare: • Open a window if it will help you to sleep. or ...if it helps you to sleep. ('Helping you to sleep' is the result of opening the window.)

• I will be angry if it turns out that you are wrong. not ...if it will turn out...' ('Turning out that you are wrong' is not the result of being angry.)

We also use if...will in requests:

• If you will take your seats, ladies and gentlemen, we can begin the meeting.

If you want to make a request more polite, you can use if...would:

• If you would take your seats, ladies and gentlemen...

In a real conditional sentence, we use if...happen to, if...should, or if...should happen to to talk about something which may be possible, but is not very likely. If...happen to is most common in spoken English:

• If you happen to be in our area, drop in and see us. (or If you should (happen to) be...)

Notice that we don't usually use this pattern in unreal conditionals which talk about impossible states or events in the if-clause:

• If the North Sea froze in winter, you could walk from London to Oslo, [not If the North Sea happened to freeze / should (happen to) freeze in winter...)

Unless is used in conditional sentences with the meaning 'if...not':

• There's no chance of you getting the job unless you apply, (or ...if you don't apply.)

• You can't travel on this train unless you have a reservation, (or ...if you don't have...)

With unless we use present tenses when we talk about the future:

• Unless it rains, I'll pick you up at 6.00. (not Unless it will rain...) 

In most real conditional sentences, we can use either unless or if...not with a similar meaning. However, we use if...not but not unless: • in most unreal conditional sentences:

• He would be happier if he didn't take things so seriously, (not ...unless he took...)

• If she hadn't gone to university, she would have gone into the police force, (not Unless she had gone...)

• when we talk about emotions:

• I'll be amazed if Christie doesn't win. (not ...unless Christie wins.)

• in most questions: • If you don't pass the test, what will you do? (not Unless you pass...)

We use unless but not if...not when we introduce an afterthought. 

• Without Philip to run it, the course can't continue - unless you want the job, of course, (not ... - if you don't want...) In written English, the afterthought is often separated from the rest of the sentence by a dash. We can use if or whether to say that two possibilities have been talked about, or to say that people are not sure about something:

• They couldn't decide whether/if it was worth re-sitting the exam.

• I doubt whether/if anyone else agrees with me.

Whether can usually be followed directly by or not.  Compare:

• I didn't know if Tom was coming or not. (not ...if or not Tom was coming.) and • I didn't know whether or not Tom was coming, (or ...whether Tom was coming or not.)

We prefer whether rather than if: • after the verbs advise, consider, discuss:

• You should consider carefully whether the car you are interested in is good value.

• before to-infinitives and after prepositions:

• I couldn't decide whether to buy apples or bananas.

• We argued about whether women are more liberated in Britain or the USA.

• in a clause acting as a subject or complement:

• Whether the minister will quit over the issue remains to be seen.

• The first issue is whether he knew he was committing a crime. 

• in the pattern noun + as to + whether to mean 'about' or 'concerning':

• There was some disagreement as to whether he was eligible to play for France.

Other nouns commonly used in this pattern are debate, discussion, doubt, question, uncertainty. These sentences include other words and phrases used to introduce conditional clauses:

• We'll have the meeting this afternoon, provided/providing (that) no-one objects.

• Supposing (that) they ask me why I resigned from my last job - what should I say?

• I'll write to you every week - as/so long as you promise to reply.