Grammar: Word classes: Verbs: Verb formation

Modal auxiliary verbs (can, could)

Talking about likely and unlikely situations

We use 'conditionals' to talk about situations which are likely and unlikely. Conditionals are introduced by the subordinating conjunction if.

If we want to talk about a likely situation, the verb in the subordinate clause is in the present simple and we use the modal verb will in the main clause. This is sometimes referred to as the 'first conditional':

If I collect enough sleep, MegaMonster will be pleased.
present simple                                                  modal verb

If we want to talk about an unlikely situation, the verb in the subordinate clause is in the past simple and we use the modal verb would in the main clause. This is sometimes referred to as the 'second conditional':

If I had wings, I would be able to fly.
  past simple         modal verb

Note that an if conditional structure is only one of many ways of presenting an unreal condition.