We use if + Present Simple + Present Simple to talk about something that is true at any time, i.e. facts:

• If babies are hungry, they cry.
• If you heat ice, it melts.
• If you mix red and blue, you get purple.

We use if + Present Simple + will + infinitive to talk about things that are possible in the future:

• We will go for a walk at the weekend if the weather is good. (= It’s possible the weather will be good.)

Note that in this sentence there is a possibility and a result:

If the result is only possible, not certain, we use might (not will):

• If the weather is good, we might go for a walk at the weekend. (= It’s possible that we will go for a walk at the weekend if the weather is good.)

We can use unless to mean if … not:

• We will go for a walk at the weekend unless it rains. (= … if it doesn’t rain.)
• Unless you study hard, you won’t pass the exam. (= If you don’t study hard, …)

We use if + Past Simple + would + infinitive to talk about the present, and to imagine something different from the real situation now:

• If I had his number, I would call (= I don’t have his number so I can’t call him.)
• If I earned more money, I would buy a house. (= I don’t earn enough money to buy a house at the moment.)
• If she was prime minister, she would invest more money in schools. (= She isn’t prime minister but this sentence imagines that she is.)

We can also use the Second Conditional to talk about an unlikely situation in the future:

• If I won a lot of money, I‘d buy a big house in the country.
• I wouldn’t give up my job if I won a lot of money.
• If I became President, I would support green energy projects.