Zero and First Cinditional

                                     Zero and First Conditional

A zero conditional sentence is made up of two halves:

If

+

Present Simple

Then

Present Simple

We use this structure when we describe what always happens as a result of something.

It is often used to describe scientific rules which are, by definition, unchanging...so the results always happen the same.

Examples:

If you take ice out of the fridge in summer, it melts.
A stone sinks if you throw it in a lake.

We can also use the zero conditional to say what we do as a rule in certain situations. Here, we are not talking about what we do in a particular, specific situation (e.g. tonight, tomorrow) but what we always do in these conditions.

If I get a headache, I go and lie down.
If I miss the train, my sister always gives me a lift to work.

                  First Conditional

A first conditional sentence is comprised of two halves.

If

+

Present Simple

Then

Will

We use the first conditional to say what we will do in a certain situation in the future.

If it rains tomorrow, I will stay at home and paint the kitchen.
They will see Harry if he comes to the dinner party.

The negative uses won't.

She won't get to know him if he doesn't come!
If we study so little, we won't pass the exam.

Don't use will with if.

If I see him, I will tell him.
NOT If I will see him, I will tell him.

Note. Compare the zero and first conditional. In the first sentence, we are talking about what you always do, it's your rule, if you like. In the second sentence, however, it is what you will do tonight, on that one specific occasion.

If there's nothing in my fridge, I ring for pizza.
If there's nothing in my fridge tonight, I will ring for pizza.

There are other expressions in English that are followed by the present simple in the same way as "if" is in first conditional sentences.
unless, when, in case, provided that, until, as soon as. See below for examples.

Unless

Meaning: except if.

I'll stay in a hotel, unless Joan lets me stay in her house for a few days.

In Case

To do something because you think something else will happen:

I'll take my credit card in case we see something we want to buy.

Provided That

This means "only if".

I'll lend you this $10 provided (that) you pay it back by Wednesday.

Until

Meaning: up to the point.

I'll wait in the hotel until you arrive.

As Soon As

We use "as soon as" to talk about something happening immediately after. Compare how "when" and "as soon as" are used:

I'll call you when my husband comes home. (I might wait ten minutes)
I'll call you as soon as my husband comes home. (I won't wait, it will be immediately)