Grammar: First and Second Conditionals

We know that it always rains in Manchester, so when it rains, you need an umbrella. Sometimes, though, we want to talk about things that are not definitely true but probably (80/90%) true. Sometimes, we want to talk about things that are possibly, but unlikely to be, true (20/30%). Look at the weather forecast for next week:

Today is Saturday. On Sunday, it's definitely going to rain. On Monday, there will probably be some sunshine. On Tuesday and Wednesday, it will be warm and sunny: it's unlikely to rain on Tuesday and Wednesday.

To talk about things that are definite,   we use a zero conditional
To talk about things that are probable, we use a first conditional
To talk about things that are unlikely,   we use a second conditional

Zero:      When it rains, people stay at home.
First:       If it's a nice day on Monday, I will go out with my friends.
Second:  Tuesday is going to be a nice day, but if it rained, I would stay at home.
All conditionals are made in a similar way. There are two halves to each conditional sentence:

Remember:

• you can use when instead of if  to make your sentence sound more definite
• you can use unless + positive sentence to say if.... not, eg

If Aziz doesn't arrive in 10 minutes, I will go home./ Unless Aziz arrives in 10 minutes, I will go home.
I'll call you later if I don't see you at breaktime./       I'll call you later unless I see you at break time.

Be careful:
If you start the sentence with IF, don't forget the comma!
Don't use the comma if you don't start the sentence with IF!

Don't use IF and WILL/WOULD in the same half of the sentence: use the comma to keep them separate.

You can practise first conditionals here: http://elt.oup.com/student/headway/preint/a_grammar/unit09/hwy_preint_unit09_2?cc=gb&selLanguage=en
You can practise second conditionals here:
http://elt.oup.com/student/headway/preint/a_grammar/unit11/hwy_preint_unit12_1?cc=gb&selLanguage=en
You can find more practise here:
http://elt.oup.com/student/englishfile/preint/a_grammar/file06/?cc=gb&selLanguage=en