Clauses of Condition talk about hypothetical events. There are three main types of clauses of condition.

1. Present real condition:

    Form: If + Present Simple, Future Simple

    Examples:

    1. If it rains, we will stay home and watch the football match.
    2. If her baby sitter arrives early, Anne might go shopping.

2. Present unreal condition:

    Form: If + Past Simple, Past Future Simple   

    Examples:

    1. If she were here, my friend Yoko would help me with this homework.
    2. If Anne had money, she would not work extra jobs for her children.

3. Past ureal condition:

    Form: If + Past Perfect, Past Future Perfect

    Examples:

    1. If my grandfather had been alive, he would have taught me to write
        a poem.
    2. If her baby had not been so cranky, Anne may have gone shopping
        with us.

    Note that other modals may be used to indicate possibility, suggestion,
    or ability.

Mixed Conditional Clauses:

Sometimes, the forms of the verbs which are used in Type 2(Present Unreal) and Type 3(Past unreal) were mixed across the board. Look at the following examples:

1. If Mary was/were that doctor, she would have helped that poor old man.
In this statement, Mary is alive and she is not a doctor. She couldn't save the man who had an accident and eventually died because the doctor didn't save him.

2. If Anne had decided to marry John, she wouldn't suffer a miserable life with Tom.
In this statement, Anne lives in misery now because she didn't marry John, although he proposed to her, and decided to marry Tom instead.

    More about Modals