If + past + would + verb
Second conditional is used in situations/actions in the present or future which are not likely to happen or are imaginary, hypothetical or impossible.
- If I won the lottery, I would travel around the world and buy a castle.
I think it is very unlikely that I will win the lottery. However, in this unlikely condition, I will travel and buy a castle.
- If I wasn’t watching TV now, I would be playing football.
I am watching TV, but I am imagining an alternative activity I would be doing if I wasn’t watching TV.
- If I were an alien, I would be able to travel around the universe.
It is impossible for me to be an alien. However, I am imagining what I would do in this situation
Other modal verbs can be used in place of would:
- If I had more money, I could buy a car.
Buying a car would be possible.
- If I won the lottery, I might give all the money to charity.
Giving the money to charity is only a possibility.