If verb như thế nào

Unless (trừ khi) đồng nghĩa với if...not. Như if, unless được theo sau bởi một thì hiện tại, một thì quá khứ, hoặc một quá khứ hoàn thành (không bao giờ bởi một điều kiện). Unless được dùng thay vì if...not trong câu điều kiện dưới mọi kiểu. Thứ tự của mệnh đề không quan trọng với câu sử dụng unless.

Kiểu điều kiện 1 : Unless + thì hiện tại

Với If	Tương đương với Unless
You will be sick if you don't stop eating.	You'll be sick unless you stop eating.
I won't pay if you don't provide the goods immediately.	I won't pay unless you provide the goods immediately.
If you don't study dilligently, you'll never understand trigonometry.	Unless you study dilligently, you'll never understand trigonometry.

Kiểu điều kiện 2: Unless + thì quá khứ

Với If	Tương đương với Unless
If he wasn't very ill, he would be at work.	Unless he was very ill, he would be at work.
I wouldn't eat that food if I wasn't really hungry.	I wouldn't eat that food unless I was really hungry.
She would be here by now if she wasn't stuck in traffic.	She would be here by now unless she was stuck in traffic.

Kiểu điều kiện 3: Unless + quá khứ hoàn thành

Với If	Tương đương với Unless
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.

What this handout is about

There are many different ways to express “conditional” or “hypothetical” meaning in English. One of them is to use the word “if” in the clause that expresses the condition. For example, “If it rains, we’ll cancel the picnic. If it doesn’t rain, we won’t.” This handout explains how different verb tenses indicate different meanings when you are speaking hypothetically and should help you choose the right verb tense for the meaning you want to convey.

Using this handout

Most explanations of the conditional don’t use one consistent example, so it’s difficult to see how different verb tenses convey different meanings. This handout uses the same basic activity in each example (sticking your fingers into the fire) to show how the situation influences the choice of verb tense. The critical factor is the *likelihood* of the situation being real. Pay attention to the situation described before each example and notice how the verb changes as the situation becomes more and more likely.

Zero conditional: “Real condition”

This conditional deals with “real” conditions. We don’t call it “real” because it has already happened: we call it real because it *always* happens this way. We use this to describe a condition with an absolutely predictable result—in other words, to state a fact.

If you stick your fingers in the fire, they get burned. (fact—happens every time)

When the situation is completely likely, use present tense in both clauses.

First conditional: “Unreal, but likely”

This conditional deals with “unreal, but likely” situations in the present or future. We call it “unreal” because situation we are describing hasn’t happened yet, and “likely” because we can easily imagine it happening. We use the first conditional to describe these situations.

For example, a 3 year old child is reaching toward the fire. She hasn’t put her fingers into the fire yet, but we know that small children don’t understand fire, so we can easily imagine her touching it. We would say:

If you stick your fingers into the fire, you will burn yourself. (Same idea as above, but rather than stating a general fact, you are talking about a specific incident.)

If you stick your fingers into the fire, you will be crying all day.

Notice that the verb “stick” is in the present tense. Using the present tense verb shows two things:

1. it hasn’t happened yet (it’s unreal)
2. you believe it could happen (it’s likely)

Also notice that the main clause verbs (will burn, will be crying) can be in simple form or -ing form. It depends on whether you want to emphasize a single moment in time (simple form) or the an extended period of time (-ing form). In either case, use will + verb in the main clause.

When the situation is unreal, but likely, use present tense in the conditional clause and will + verb in the main clause.

Second conditional: “Unreal and unlikely”

This conditional deals with situations in the present and future that are both unreal and unlikely. The situation we are describing hasn’t happened yet, and we really can’t imagine it happening very easily, except in a freak accident or a moment of great stupidity.

For example, a 25 year old is joking about reaching into the fire. He hasn’t put his fingers into the fire yet, and we don’t think he’s serious about doing it, but we want to warn him about the consequences just in case. We would say:

If you stuck your fingers into the fire, you would need medical attention.

If you stuck your fingers into the fire, you would be screaming in pain all day.

Notice that the verb “stuck” is in the past tense. Using the past tense verb shows two things:

1. it hasn’t happened yet (it’s unreal)
2. you don’t really believe it will happen (it’s unlikely)

Also notice that the main clause verbs (would need, would be screaming) can be in simple form or -ing form. It depends on whether you want to emphasize a single moment in time (simple form) or the an extended period of time (-ing form). In either case, use would + verb in the main clause.

When the situation is unreal and unlikely, use past tense in the conditional clause and would + verb in the main clause.

Third conditional: “Unreal condition”

This conditional deals with situations in the *past* that are unreal—they didn’t happen. We can still imagine what the consequences would have been.

For example, the 25 year old was joking about reaching into the fire, but he didn’t actually do it. We would say:

If you had stuck your hand into the fire, you would have needed medical attention.

If you had stuck your hand into the fire, you would have been screaming in pain.

In the next two examples, the 25 year old actually did stick his hand into the fire. The “unreal” situation is the opposite:

If you hadn’t stuck your hand into the fire, you wouldn’t have spent the evening in the emergency room.

If you hadn’t stuck your hand into the fire, you wouldn’t have blistered it so badly.

When the situation is unreal and in the past, use past perfect (had + -ed) in the conditional clause and would have + verb in the main clause.

Mixing time references

In the examples of the third conditional (unreal and in the past), both the conditional clause and the main clause refer to past time: If you had done this in the past, you would have experienced this in the past.

It is also possible to mix time references—to talk about a condition in the past and the consequences in the present. For example:

If you had stuck your fingers into the fire last night, you would be in a lot of pain right now.

If you hadn’t stuck your fingers into the fire last night, you wouldn’t be wearing bandages today.

Find more examples at the English Club website: http://www.englishclub.com/grammar/verbs-conditional.htm

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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 License.
You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill

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