When we are thinking about a situation in the present or future that is hypothetical, unlikely or impossible, we use:
If + Past Simple, ...Would + Verb
We use a past verb though are imagining the present or the future to be different.
The second clause of subject + would + verb (conditional verb) is conditional to the first clause happening (or will only happen if the first part/clause happens).
Example: If I won the lottery, I would travel around the world.
= It is unlikely that I will win the lottery, but I'm going to hypothetically imagine that I did win. In that situation I would travel around the world. So in order for me to travel around the world, I would need the first clause (the condition or situation) to happen, that is, for me to win the lottery first.
- If I won the lottery, I would travel around the world. (Though I am unlikely to win the lottery)
- If I knew his name, I would tell you.
- If I didn't have a headache, I would go to the party.
- If I became President, I would reduce the salaries of all politicians. (Though it is unlikely I will become President)
Notice how we use a comma after the past tense clause.
We can also reverse the order and use:
Conditional verb (would + verb) + If + Past Simple
- I would be happy if I had more free time.
- I would tell you the answer if I knew what it was.
- There would be fewer accidents if everyone drove more carefully.
- We would have a lot of money if we sold our house.
- Would she come if I paid for her flight?
- Would you accept the job if they offered it to you?
- What would you do if you won the lottery?
- What would you do if you saw a U.F.O?
Notice how the comma is not necessary with this word order.
If I were ...
Note that with the verb To Be we use IF + I / HE / SHE / IT + WERE
The reason we use WERE instead of WAS is because the sentence is in the Subjunctive mood.
- If I were not in debt, I would quit my job.
- If he were taller, he'd be accepted into the team.
- She would be still be correcting my grammar if she were still alive.
Though in informal English, you will hear some people say If I was... If he was... etc. This usage doesn't sound good though unfortunately is common.
