Here's the sentence that's been confusing me:

Compared to dogs, cats showed more enthusiasm.

I feel this should be a complex sentence because there's one independent clause and one dependent clause. But there is no subordinating conjunction here.

Now consider

When compared to dogs, cats showed more enthusiasm.

This one fits the definition of a complex sentence (independent clause, dependent clause, and a subordinating conjunction "when").

My question is this: how to detect complex sentences of the former type?

  • 2
    Not all subordinate clauses have subordinating conjunctions. Only adverbial clauses use those. Noun clauses, aka Complement clauses use complementizers like for...to for infinitives and that for tensed clauses (He likes for me to stack it over there; He said that I did well). Adjective clauses, aka relative clauses, use relative pronouns like which or that. These are not conjunctions.
    – jlawler
    Commented Sep 19, 2014 at 0:48
  • Agreed, but as per the definition of a complex sentence, the dependent clause needs to be joined by a subordinating conjunction. Please correct me if this should not be a requirement for a sentence to be complex. Commented Sep 19, 2014 at 1:47
  • 1
    Footnote to jlawler's commment: As I'm sure jlawler knows, English complementizer & relative "that" can be dropped in some contexts. Hence "He said I did well." "The woman I knew left town." Commented Sep 19, 2014 at 2:29
  • 1
    @ChthonicProject: If the definition of "complex sentence" requires a subordinating conjunction, then the definition of "complex sentence" is simply incorrect, and no one should pay attention to it. Either that, or everyone should realize that saying something is a "complex sentence" says precisely nothing about it.
    – jlawler
    Commented Sep 19, 2014 at 3:35

4 Answers 4


The question is struggling with what school grammar (the type of grammar that many of us were taught in middle school) considers to be a clause as opposed to what theories of syntax consider to be a clause. According to school grammar, a complex sentence consists of two or more clauses, where a clause is generally understood to contain at least a subject and a predicate, e.g.

 When one considers the reactions of the dogs, the cats showed more interest.

This sentence has two clauses, each of these clauses containing a subject and predicate. The first clause, i.e. when one considers the reactions of the dogs, contains the subject one and the predicate considers the reactions of the dogs, and the second clause, i.e. the cats showed more interest, contains the subject the cats and the predicate showed more interest. The latter clause is the main clause, and the former clause the subordinate clause.

What one should be aware of in this area is that school grammar simplifies and bunches concepts so that they can be presented to young minds more easily. When one studies these distinctions in some detail, one quickly sees that the traditional definitions do not work very well. The question has touched on just such an aspect of clauses where one can see that the traditional definitions do not help so much.

The clause concept is much more extensive than what the question assumes. In othe words, the question is proceeding from too narrow of a definition of the clause. The example sentence contains what can be construed as a nonfinite clause. Further examples of nonfinite clauses follow:

 a. Disgusted with the situation, he stormed out of the room.

 b. She worked all night, having no choice.

 c. Being required to work on Wikipedia articles upset the students.

These sentences contain the constituents disgusted with the situation, having no choice, and being required to work on Wikipedia articles, whereby these constituents can be interpreted as the predicates of clauses. The subjects of these clauses are implied, i.e. they are easily understood from the context. For sentence a, "he" is the one who was disgusted with the situation; for sentence b, "she" is the one who has no choice; and for sentence c, "the students" are the ones who are required to work on Wikipedia articles. Like most languages, English has mechanisms in place that allow it to express predicates without also having to state the subjects, since the subject is easily retrieved from the context.

If one desires a formal linguistic concept for the issue at hand, it is control. The theory of control explores when the subject of a predicate has to be expressed overtly and when it can be implied from the context. In any case, one is dealing with clauses because the subject is present (either overtly or covertly).

Finally, the notion that a subordinate clause must be introduced by a subordinator (= subordinate conjunction) is wrong. While it is true that many subordinate clauses are indeed introduced by a subordinator, there are types of subordinate clauses that are not introduced by a word that is taken to be a subordinator, e.g. relative clauses and indirect questions.


These are SIMPLE SENTENCES. These are not complex sentences because they don't have a dependent clause. Any type of clause should have a subject and a verb (an action / conjugated verb). A dependent clause must additionally contain a conjunction to connect it to the main clause and a meaning that supports the information of the independent clause. Otherwise it's a phrase.'Compared to dogs'is a prepositional phrase ( to+object) that is starting with a past participle. Don't mistake 'compared' as an action verb. Action verbs have a subject that is doing the action. Who is comparing the cats to the dogs? No one. Hence, the action verb here is 'showed'.

For instance: When compared to dogs (conjunction hence dependent clause) When we compare dogs to cats (dependent clause because we is subject doing the action verb 'compare') So, these are all simple sentences :) I'm sure you would've found that in 5 years.


What one should be aware of in this area is that school grammar simplifies and bunches concepts so that they can be presented to young minds more easily.

Tim Osborne's answer is absolutely to the point, I'd only add a small comment on the part above. I don't see how bunching disparate concepts together can help anyone, young or old, understand the workings of language. And can't say in which way it makes the model simpler, easier or more approachable to the learner. Finding the way through the daunting terminological complexity involving subordinating conjunctions, complex, compound, complex-compound clauses etc. presents a huge challenge in itself, and it is exactly what gave grammar a bad name.

(I would have commented on Tim Osborne's post, if I had enough reputation)


Both "When compared to dogs," and "Compared to dogs," have no subject and are therefore phrases rather than clauses. The sample sentences are simple sentences having one independent clause. These are not complex sentences.

In these sentences "When compared to dogs," and "Compared to dogs," are adverbial phrases.

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