Mixed Conditionals

Use:       

Mixed conditional sentences combine two different conditional patterns. 
Several patterns can be used:

• mixed first conditional sentences

First conditional sentences can use a variety of modal verbs.
If + present simple, can / may / might / will / should + verb (infinitive)
If you give me some money, I can buy some milk.
If I finish my homework, may I go out with my friends?
If you switch the photocopier off and on again, it should work.

First conditional sentences can also use going to, as well as will.
If + present simple, going to + verb (infinitive)
If you don’t get ready soon, we’re going to be late!

The present continuous and going to can also appear in the If clause
If you’re going to the shop, can you buy me some cola?
If you’re going to pay him, make sure you get a receipt.

The present perfect may also appear in the If clause.
If you’ve finished your work, you can go home.

• mixed third / second conditional

This combination describes an imagined event in the past and the present result. 
If + past perfect, would + verb (infinitive)
If he'd taken the medicine, he wouldn't still be sick.
He wouldn’t still be sick if he’d taken the medicine.

• mixed second / third conditional

This combination describes a situation which is never true, and the past consequence of this situation.
If + past simple, would have + verb (infinitive)
If you were better at speaking in public, the presentation would have been more successful.
The presentation would have been more successful if you were better at speaking in public.