Subordinate clauses connect a main clause to a subordinate clause, making the subordinate syntactically depend on the main one. They indicate the logical relation between the two clauses, such as cause, time, condition, purpose, comparison, concession, or consequence. The meaning of the sentence depends on the conjunction chosen, because it defines what kind of information the subordinate is bringing. In Portuguese, we use these conjunctions to organize the text and avoid loose or ambiguous sentences.

Causal conjunctions introduce a clause that explains the motive or reason behind what appears in the main clause. The relation expressed is explanatory: the subordinate presents the cause and the main clause provides the result or fact. In general, the causal clause can appear before or after the main one without changing the logical sense, only the focus of the information.

Conditional conjunctions introduce a clause that presents a hypothesis, condition, or requirement for the idea of the main clause to take place. The relation is one of dependence: if the condition is met, the content of the main clause may occur. Normally, the conditional subordinate clause is started by the conjunction and can use verb tenses such as present, the future subjunctive, or the imperfect subjunctive, depending on the degree of certainty or possibility.

Temporal conjunctions introduce a clause that situates in time the fact of the main clause, indicating when something happens. The subordinate can mark anteriority, simultaneity, or posteriority relative to the main. The temporal value may require different verb tenses to show the order of events clearly.

Final conjunctions introduce a clause that indicates the objective or intention of what is in the main clause. The subordinate answers the question 'for what' and, in Portuguese, normally uses the verb in the subjunctive when the purpose is hypothetical or depends on realization. The use of a preposition before the conjunction may appear with or without an article, depending on the structure of the sentence.

Concessive conjunctions introduce a clause that admits an idea contrary or an obstacle, but without preventing what is in the main clause. The relation is one of contrast: even with the concession, the fact of the main clause remains. In many cases, the concessive subordinate uses the subjunctive to mark the idea of possibility or generalization.

Consecutive conjunctions introduce a clause that expresses the result or effect of what is in the main clause. The main clause typically includes an intensifier, and the subordinate completes it with the consequence. In Portuguese, the structure "tão… que" or "tanto… que" is very productive to indicate consequence clearly.

Comparative conjunctions introduce a clause that establishes a comparison with the term of the main clause. The subordinate completes the comparative sense started in the main clause and, in many cases, may allow omission of repeated words for economy. The sense can be equality, superiority, or inferiority, depending on the terms used.

Subordinate conjunctions organize the meaning between clauses, marking relations such as cause, condition, time, purpose, concession, consequence, and comparison. The choice of conjunction determines what type of information the subordinate clause conveys and how the reader interprets the link between ideas. Mastering these groups allows you to build clearer and more cohesive sentences in Portuguese.