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Guide to English Grammar for international learners & teachers of English



Conditional sentences

The most common kind of conditional sentence that you are likely to meet will contain two clauses, one of which will start with the word if, as in If it rains, we'll have to stay at home. The clause without the if is the main clause of the sentence, while the if clause is subordinate. The order of the two clauses is generally not that important to the meaning of the sentence; so we can switch the if clause to the end of the sentence if we want to.

Most grammar books tend to recognise four basic configurations of tenses in conditional sentences which vary in structure according to the time that we are talking about (past, present or future) and the meaning. These four types are normally referred to as the zero, first, second and third conditionals; we will look at the forms and meanings of each of these in turn and also examine some of the alternatives to these four basic types.

Zero-type conditionals

Form and meaning

The form of the zero conditional causes no problems since the present tenses are used in both clauses.

Zero-type conditionals

If clause

Main or conditional clause

If + Present tense

Present tense

If you heat water

it boils.

The zero conditional is normally used to talk about facts and to express general truths.

First-type conditionals

Form and meaning

The basic form for this type of conditional sentence can be seen in the chart below. As before, the order of the clauses can be changed with no change in meaning.

This type refers to future possibilities that are certain or probable.

First-type conditionals

If clause

Main or conditional clause

If + Present tense

Future tense

If they don't arrive soon

If they are late

we'll leave without them.

I'm going to be angry.

You will note that on the if side of the sentence any present tense can be used, while in the main clause the speaker is free to choose any future that helps to express any additional meaning that the speaker wants to express.

If he's sleeping, he won't wake up until morning. (The Present Continuous in the first part of the sentence expresses the present temporary nature of the situation and the will in the second part is making a prediction about the future.)

Alan is going to post me the recipe, if he finds it. (In the first clause I am expressing Alan's intention so going to is the best future to use, while the second clause contains a Simple Present tense.)

If he's staying at the party, I'm leaving. (In the first clause I am thinking about the possible current state of affairs, so I choose the Present Continuous, while in the second I am referring to the future plan that I have in mind should he decide to stay, so again I choose the Present Continuous.)

If you have finished the essay, leave it on my desk. (By using the Present Perfect tense in the if clause I am stressing the completed nature of the action, while in the second clause I have used an imperative, which has a future meaning.)

Second-type conditionals

Form and meaning

This type is often called the hypothetical or 'unreal' future conditional since it is usually used to speculate about either very unlikely future situations or present and future impossibilities.

Second-type conditionals

If clause

Main or conditional clause

If + Past tense

would + verb

If I had time

If I had wings

I would drop you off at school.

I would fly.

Other examples are:

Third-type conditionals

Form and meaning

This type refers to hypothetical situations in the past. In this case we use the Past Perfect tenses in the if clause and would + have in the main clause.

Third-type conditionals

If clause

Main or conditional clause

If + Past Perfect tense

would have + past participle

If I had known about his condition

If we had known about the storm

I would have phoned for you earlier.

we wouldn't have started our journey.

The main uses of the third conditional are for speculating about the past, expressing regrets, excusing our own actions and criticising others. Some of the uses tend to overlap in practice as the examples below demonstrate:

There is one other major variation to the form given in the chart above; in place of the more usual

If I had known about his condition...

we can use

Had I known about his condition... where the if is omitted and the subject and auxiliary verb are inverted.

Mixed conditionals

The four types of conditional sentence discussed above appear to fit into very rigid patterns of form and meaning but we often find exceptions to these rules. In many cases we may want to talk about events that happened or did not happen in the past and the present results of those events. Therefore, we will often need to mix clauses from different conditional types in order to get our meaning across clearly and unambiguously. Taking one example from above, we might want to say:

If I'd bought the lottery ticket, we would be millionaires now.

In this sentence I want to refer to something that I did not do in the past (and probably regret) and the possible effect that this action might have had on the present - so I use a third-conditional if clause and a second-conditional main clause. Swapping around these two types we also get:

This kind of mixing of conditional types is not uncommon.

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