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 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.
See our grammar notes about IF I WERE YOU...
Could in Second Conditional sentences
COULD can be used instead of WOULD to make the hypothetical present or future more likely.
If he trained every day, he could represent his country
If I had a little more money, I could buy a car.
