This will be short, I hope. I think it’s time to define for my fine readers what “complex” means, grammatically speaking.
A complex sentence contains at least one subordinate clause.
Your eyes glazed over. I saw it. So here it is in plain language, following an example.
My brother, who was the valedictorian of his class, just lost his job.
That clause in italics is subordinate, meaning it can’t stand alone as is as a complete sentence because it’s directly related to another word, in this case a noun, in the sentence. It’s also called a dependent clause because it depends on the rest of the complete sentence to make sense.
When grammarians, some of whom are editors, talk about complex sentences, this is what they’re talking about. There’s another dependent (subordinate) clause. “Some of whom are editors.” There’s a subject, “some,” and a verb, “are.” You can’t just say “Some of whom are editors” and have a complete sentence, though. What does “some” relate to? “Grammarians.” Pull out that dependent clause, and you still have a complete sentence: When grammarians talk about complex sentences, this is what they’re talking about.
In fact, that sentence begins with a subordinate (dependent) clause: “When grammarians talk about complex sentences” can’t stand on its own as a complete sentence. Even taking out the subordinate clause beginning with “some” leaves us with a complex sentence. “This is what they’re talking about” is the independent clause, the complete sentence, the base on which the rest is built.
Sure, we speak in dependent clauses when we’re being informal, especially if we’re adding information to what someone’s saying. But grammatically? They’re not sentences, and they can’t stand alone.
Just because a sentence contains a lot of words doesn’t mean it’s grammatically complex. It may just have a lot of words.