What characterizes a complex sentence?

A complex sentence is characterized by the presence of a main clause and one or more subordinate clauses. The main clause can stand alone as a complete thought, while the subordinate clause cannot; it relies on the main clause for its meaning. This structure allows for more nuanced expression and can convey relationships between ideas, contrasting with simpler sentence structures.

In contrast, a sentence that contains no clauses cannot be classified as a complex sentence since it lacks the necessary components of a main or subordinate clause. A sentence with two or more independent clauses aligns with the definition of a compound sentence rather than a complex one. Lastly, a requirement for having at least two complete thoughts does not specifically define a complex sentence, as it may include a main and a subordinate clause without necessitating multiple independent clauses. Thus, the defining feature of a complex sentence is indeed the inclusion of at least one subordinate clause alongside a main clause.