The most important context where the conditional is used are conditional clauses. We distinguish three types of conditional clauses. In a conditional clause of type I the conditional is not used and we can distinguish between an unaccomplished action and an accomplished action.
conditional clause of type I: The condition is possible
If he reads the book, he will know more.
If he has read the book, he will know more.
In a conditional clause of type II we have always an unaccomplished action, because if the action is accomplished, it becomes a conditional clause of type III.
Conditional clause of type II: The condition is possible, but not probable
If he read the book, he would know more.
Conditional clause of type III: The condition impossible
If he had read the book, he would have known more.
Concerning the conditional clause of type I there is a difference compared to other roman languages and English. In the if-part of a conditional clause I other roman languages use the present indicative if the condition is described as unaccomplished and present perfect indicative if the condition is described as accomplished and in the main sentence the present indicativ or the futur indicative in the main clause.
In Portuguese we use the futuro do conjuntivo in the if clause of conditional clauses I. This contradicts a little bit to what has been said in the chapter about the futuro do conjuntivo, because it is questioned whether or not the event described in the main clause will occur. However we don't have a subjective evaluation. If the condition is given, the event described in the main clause will happen. There is an objective relationship. (At least the person who makes this statement believes that.)
Actionally we can find that Portuguese is more logical than other languages regarding this point. There is no doubt that the condition is only a possibility, not a fact. The conjunctive is therefore the more logical option. We can only discuss whether the presente do conjuntivo or the futuro do conjuntivo would be more logical, but in any case the Portuguese think that the futuro do conjuntivo is more logical.
Select in the following sentences the right option. You can deduce the type of conditional clause from the main clause. If the indicative in the main clause is used, it is a conditional clause of type I. If in the main clause the conditional I is used, it is a conditional clause of type II. And if in the main clause a conditional II is used it is a conditional clause of type II. (Obviously you can deduce that as well from the English sentence.)
In conditional clauses of type I we use the futuro I / II do conjuntivo.