Conditional sentences

1. Variation in verb tenses

There are many possible sequences of tense in conditional sentences, but the four commonest and the most useful ones are represented as the four types of conditional sentences:

1.0. Type 0: real condition

These sentences are statements of universal truth or general validity in the present or past. Statements in this form commonly appear in factual discussions or explanatory (particularly scientific and technical) material.

The tense form of the verbs is determined by the time reference.

present + present for what is always true:

If you heat ice, it melts.

If I make a promise, I keep it.

If the water is boiling/has boiled, it means the food is nearly ready.

past + past for situations in the past

If he made a promise he kept it.

If it was snowing, we stayed at home.

In this type of sentence, if corresponds closely in meaning to when(ever).

1.1.Type 1: real condition referring to the future (open condition)

In these sentences, the conditional clauses represent 'open' conditions; that is, conditions that may or may not be fulfilled. We make such statements when the action or event mentioned in the conditional clause appears likely to happen.

The commonest sequence of tenses in this type of sentence is:

If clause main clause

present tense Future

(simple, continuous, Modal verb

or perfect) Imperative

If we catch the 10 o'clock train, we shall get there by lunch-time.

If you wake up before me, give me a call.

If you keep driving like that, you're going to have an accident.

If she has finished work by 4 o’clock, she will go home.

1.1.1. Type 1: variations

1.1.1. If (you) should

In a real conditional sentence, we use if…should, if…happen to, or if...should happen to to talk about something which may be possible, but is not very likely.

We may call this a condition of remote possibility, and this variation can be used in any conditional clause of this first type. If…happen to is most common in spoken English:

If you happen to be in our area, drop in and see us.

If we should miss the 10 o'clock train, we shan't get there till after lunch.

It is possible to substitute by any chance for should, without changing the meaning

If by any chance-we miss the 10 o'clock train, we shan't get there till after lunch.

1.1.2. If (you) will/would

Will is not used in the conditional clause as an auxiliary indicating future, even though the sentence has a future time reference. Will can only be used as a modal verb to introduce the idea of 'your' agreeing, or being willing, to do what is suggested.'

In this meaning will is used:

- in polite requests meaning if you agree

If you will reserve seats, we shall be sure of a comfortable journey.

If you will/would wait here, I'll see if Mrs Green is free.

- for emphasis, meaning 'insist on doing'

If you will stay out late, no wonder you are tired! (insist on staying out)

- when we talk about a result of something in the main clause

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.)