Must (obligation, prohibition)

Must is a modal auxiliary verb. It is followed by a main verb. The structure is:

subject + must + main verb

In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary.

I must stop smoking.

We can use must to talk about the present or the future. Look at these examples:

I must go now. (present)

I must call my mother tomorrow. (future)

We cannot use must to talk about the past. We use have to to talk about the past.

1. Conditional zero and first

TYPE O: GENERAL CONDITION.

The 0 (zero) conditional is the easiest to understand! It is also called the real or factual conditional because it is used to talk about facts, or something that is always true.

If / unless+ Subject+ Present tense+ Subject+ Present tense

If I eat too much, I get sick.

The result [ I get sick ] is always true of the condition [ if I eat too much ]. It is a fact! There is a fixed connection between the two events.

This conditional is easy because we don’t have to remember which clause goes where or which verb tense is used, we just have to remember: facts, habits, daily routines, rules, general truths = present simple

If you mix yellow and blue, you get green.

We can also use modals in the result clause:

If you want to go to university, you must study hard.

Notice that 'unless' means the same as 'if not'.

Unless prices are rising, it's not a good investment.

TYPE 1: REAL CONDITION

This type of condition shows that it is still possible for the event or the action to happen. It is called “ Conditional Clause- Type 1”.

If / when/ unless+ Subject+ Present tense+ Subject+ Will Can May+Infinitive verb

without “to”

- If my friend invites me, I’ll visit him.

- I will visit my friend if he invites me.

Unless = [ If + not ]

If you don’t study hard, you’ll fail.

Unless you study hard, you’ll fail.

There is a difference between If and When?

A) If he comes, I will tell him the truth.

B) When he comes, I will tell him the truth.

When we use if, we are not sure about the event to happen or not.

But when we use when we are sure about the event to happen.

Variations to Type 1:

a) Variations of the main clause: may/might, may or can, must/should

b) Variations of the if-clause: Pr. Cont, Pr. Perf

1. Conditional second and third

TYPE 2: UNREAL CONDITION

This type of condition shows that it is impossible for the event or the action to happen. It is called “ Conditional Clause- Type 2 ”.

If / unless+ Subject+ Past tense+ Subject+would/could/might+Infinitive verb

without “to”

- If I were you, I wouldn’t waste my time.

Variations to Type 2:

a) Variations of the main clause: might/could, Cont. conditional form, Past Simple

b) Variations of the if-clause: Past Cont, Past Perf

TYPE 3: IMPOSSIBLE OR CONTRARY TO FACT CONDITION

This type of condition shows that it is contrary to fact. It is called “ Conditional Clause- Type 3 ”.

If / unless+ Subject+ Past Perfect (had+III form)+ Subject+would/could /might+have+ III form

- If the weather had been bad, we would have canceled the meeting.

- If they have enough time, they will finish the work. [ Type 1 ]

- If they had enough time, they would finish the work. [ Type 2 ]

- If they had had enough time, they would have finished the work. [ Type 3 ]

Variations to Type 3:

a) Variations of the main clause: could or might(instead of WOULD)

b) Variations of the if-clause: Past Perf Cont

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