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Third grade teacher here. I plan to teach students to distinguish between simple, compound and complex sentences — but only if I can demonstrate a clear and meaningful difference between the latter two!

Complex or Compound? Each sentence in the following pairs is similar to its partner.

  1. All dogs are mammals, so huskies are mammals.
  2. All dogs are mammals, therefore huskies are mammals.
  3. I come bearing soup, for Kate is sick.
  4. I come bearing soup, because Kate is sick.

Are the sentences above complex or compound?

First, we need to decide whether each italicized clause is independent or dependent. To me, they all look dependent. If that is the case, there's not much need to teach about compound sentences. Is there a meaningful difference between the sentences in each pair that I am missing? (Are the FANBOYS as special as they'd like to think?)

Thank you,


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3 Answers 3

It depends on your teaching purpose. Notwithstanding Pitarou's comments and link about FANBOYS, it may well be appropriate for third graders to learn that sentences whose two clauses are connected by one of the FANBOYS (coordinating conjunctions) are called compound sentences. Sentences whose two clauses are joined by one of the other (subordinating) conjunctions are called complex sentences.

Hence in your list sentences 1 and 3 are compound, and sentence 4 is complex. Sentence 2 is somewhat problematic, since therefore is an adverb and some strict grammarians would object to it being used to join clauses thereby producing a run-on or comma splice.

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In other words, it's important for students to learn how to recognise a dependent and an independent clause. Unfortunately, FANBOYS is not a reliable guide in this matter. Is there a helpful mnemonic to remember which is compound and which is complex, because I always get those two confused. –  Pitarou Jun 6 '13 at 3:03
@Pitarou. FANBOYS can be used to identify what traditional grammar calls compound and complex sentences, if this is what the teacher wants her grade 3 students to be able to do as an introduction to English syntax (although I personally would stick to the unproblematic coordinators and, but, or, and a few common subordinators). I agree with you, however, that this in itself is of much less importance than understanding that you cannot string independent clauses together without a conjunction (run-on) or write stand-alone dependent clauses (fragment). .... –  Shoe Jun 6 '13 at 4:58
A useful indicator of coordinators/subordinators is that you can follow a coordinator with a subordinator but the reverse is not possible. For example, you can say but when or so because but not when but or because so. –  Shoe Jun 6 '13 at 4:59

Your intuitions are correct: FANBOYS is not all its cracked up to be.

I don't claim any special authority on the matter, but your examples all look to me like they are functioning as independent clauses.

Here's the first part of an article in which a linguist explodes the myth of FANBOYS. Unfortunately, the author was recently obliged to remove the latter half from his blog when he published it in a journal: suffice to say that he demonstrates that FANBOYS is arbitrary, unreliable, and unhelpful.

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In my book, sentences 1 - 3 are compound, though sentence two is punctuated incorrectly. "Therefore" is a conjunctive adverb that requires a semi-colon before it and a comma after it. But conjunctive adverbs, like FANBOYS, are both ways of linking independent clauses, and, therefore, we call them compound sentences.

Your last sentence uses the subordinating conjunction "because." With the use of "because," the second clause becomes a dependent one. It can't stand alone: "Because Kate is sick" is an incomplete thought. That's why this is a complex sentence.

Also note that you will never use a comma before a because clause (unless you have some quirky interrupter right before it). In fact, you will rarely use a comma before any dependent word when the dependent clause follows the independent one.

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