Subordinate Clauses: Conditional Clause

The "conditional clause" is a dependent clause that expresses a condition in order to happen or not happen the event of the main clause.  

The conditional conjunctions are:

• if
• unless

Some obsenvations:

1) There are three main types of conditional clauses:
        1) Possible Condition                
             if + Simple Present,                  will-Future
             If I find her address,               I’ll send her an invitation.

        2) Unlikely Condition            
              if + Simple Past,                       would + infinitive
             If I found her address,            I would send her an invitation.

        3) Impossible Condition
              if + Past Perfect,                      would + have + past participle
             If I had found her address,     I would have sent her an invitation.

2)  Unless means "if not":

• Unless you call watching TV a hobby, he hasn't got any hobbies. (If you don't call watching TV a hobby, he hasn't got any hobbies.);
• I won't have an operation unless surgery is absolutely necessary. (I won't have an operation if surgery is not absolutely necessary.)