·The rule that works for all of them
Conditionals and wishes in English. There is one rule that works for almost all of them: the if part steps back one tense from what you want to say, and will or would stay in the other part. In Spanish you say si llueve, me quedaré, and your ear expects a future. In English, after if, never will or would. We will look at the zero, first and second conditionals, the third, the mixed ones, wish and if only, and the words unless and as long as. The rules are AptisBot's own criteria.
1/5Zero, first and second
Zero conditional: if plus present, present. Something that always happens or a rule: if you heat ice, it melts. First conditional: if plus present, and will in the main clause. A real possibility in a specific case: if it rains tomorrow, we'll stay at home. And the pitfall: if she will come does not exist, it is if she comes. Second conditional: if plus past simple, and would plus infinitive. Something unlikely or imagined: if I had time, I would help you. With be, were for all persons, especially in advice: if I were you, I would apologise.
2/5Third conditional
Third conditional: if plus past perfect, and would have plus participle. It talks about something that did not happen in the past and its imagined result. If I had known, I would have come. That is: I did not know, and I did not come. The most common pitfall is to put would after if as well: if I would have known is a mistake. In the if part, had plus participle; in the other, would have plus participle. And in formal register, you can invert without if: had I known, I would have come.
3/5Mixed conditionals
Mixed conditionals. Sometimes the time of the condition and that of the result do not match. First combination: a cause in the past with a result in the present. If plus past perfect, would plus infinitive. If I had studied medicine, I would be a doctor now. I studied something else, and today I am not a doctor. Second combination: a present state that explains something in the past. If plus past simple, would have plus participle. If I weren't so shy, I would have asked her. I am shy, and I did not ask her. The question that decides: when is the condition, and when is the result?
4/5Wish and if only
Wish and if only: wishes and regrets. The idea is a step back in time. Wish plus past simple: a present you do not like. I wish I had more spare time. Wish plus past perfect: a past that cannot be changed. I wish I had studied more. And wish plus would: something that bothers you about others, or a change you want. I wish you would stop talking. If only says the same thing with more force: if only I had listened. With be, were for all persons: I wish I were taller. And do not confuse wish with hope: I hope it doesn't rain, with the present.
5/5Unless, provided that and as long as
Three words that replace if. Unless means if not: unless you hurry, you'll miss the train. And since it is already negative, you do not say unless you don't hurry, which is the typical mistake of someone translating si no. As long as and provided that, or providing that, mean only if, on condition that: you can borrow my car as long as you drive carefully. And with when and as soon as the same happens as with if: the future goes in the present. I'll call you as soon as I land.
·To practise
To practise, write six sentences of your own: a first conditional, a second, a third, a mixed one, one with wish and another with unless. Then check each one with the same question: what comes right after if? If there is a will or would, change it. And if you hesitate between two tenses in a Core question, ask yourself when the condition is and when the result is.