Complex sentences connect two or more ideas into a single sentence using coordination or subordination. A sentence may have more than one verb, each with its own nucleus and complements. Clarity depends on the order of the terms and the correct use of connectors. Punctuation marks the boundaries between parts of the sentence and helps avoid ambiguity.

Coordination joins clauses of equal value, forming sentences with no structural dependency between the parts. The most common coordinating connectors express addition, choice, opposition, explanation or conclusion. Each coordinated clause can, in general, be understood in isolation within the context of the sentence.

Coordinating connectors establish relations such as addition, alternative, opposition, explanation and conclusion. The choice of connector defines the logical sense between the clauses. Some connectors require a comma before or around, according to standard rules.

Subordination creates a relationship of dependence in which one clause completes the meaning of another. The main clause is the basis of the meaning, and the subordinate clause functions as a term within it. Subordinate connectors introduce the subordinate clause and determine its syntactic and semantic role.

Subordinating connectors indicate that a clause depends on another and define the type of subordination. In noun subordinate clauses, connectors such as 'that' and 'if' tend to appear. In adjective clauses, 'that' refers back to a term and, in adverbial clauses, expressions such as 'because', 'when' and 'if' mark circumstances.

Punctuation in complex sentences marks the boundaries between clauses and clarifies logical relationships. Commas typically separate coordinated clauses with 'but' and explanatory clauses with 'because' when they appear in the middle of the sentence.

Subordinate clauses can be classified by the role they play in the sentence: noun clauses, adjective clauses, or adverbial clauses. The noun clause completes a verb, noun, or adjective, functioning as subject, object, or complement. The adjective clause qualifies a term and can be restrictive or explanatory; the adverbial expresses circumstance such as time, cause, condition or concession.

The order of terms in complex sentences affects clarity and can change the informational focus. Fronted subordinate clauses highlight the circumstance and are generally separated by a comma. Maintaining clear references, especially with pronouns and with 'that', avoids ambiguity in long sentences.

Complex sentences in Portuguese use coordination to join ideas of equal value and subordination to create dependency between clauses. Appropriate connectors and correct punctuation support the sense and clarity of the text. Mastery of these structures enables building cohesive and precise sentences.