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MCCC Students' Pages>
Sentence Punctuation: Basics
This section does not attempt to explain all rules of punctuation, only those pertaining to connecting or separating clauses in a sentence. (For another overall view, see Study Guide 3, an online version of which is in our entry in the Writers' Guide titled Sentence Patterns.)
CONNECTING AND SEPARATING INDEPENDENT CLAUSES
An independent clause has a subject and verb, and it states a complete thought. Compound sentences consist of two (or more) such clauses. One very common way to connect these clauses is to use a coordinating conjuntion (and, but, so, yet, for, nor, or). When we do this, a comma usually comes at the end of the first independent clause and before the coordinating conjunction. (Journalistic style often omits this comma, but it is still required in formal writing.) Thus, we have:
The comma is the weakest mark of punctuation, but it is an important one.
The omission of a comma may affect meaning, so we need to be careful.
Punctuation is important, for it helps us to understand what we are reading.
Some students omit or misplace punctuation marks, and this makes their sentences confusing.
We do not ordinarily connect two independent clauses with only a comma. This error is a comma splice (a type of run-on), and it is discussed in detail in Avoiding Comma Splices.
Another way to connect two independent clauses is to use a transitional phrase or word to show the relationship of the second clause to the first clause. For instance, we may use the word however or the phrase on the other hand instead of the coordinating conjunction but) to indicate that the second clause (idea) is a contrast or contradiction to the first. In such cases, we place a semicolon at the end of the first clause (before the transitional word or phrase) and a comma after the transitional word or phrase. (Many textbooks call these transitional words "conjunctive adverbs.") Thus, we have:
The comma is the weakest mark of punctuation; however, it is an important one.
The comma is the weakest mark of punctuation; on the other hand, it is an important one.
The omission of a comma may affect meaning; therefore, we need to be careful.
The omission of a comma may affect meaning; consequently [or as a consequence], we need to be careful.
Some students omit or misplace punctuation marks; as a result, their sentences are confusing.
Unlike coordinating conjunctions, which are fixed in place between the two clauses, transitional words and phrases are often moveable. We cannot move but, so, for, and and in our four examples that use coordinators as links, but we can move the transitional words and phrases in the sentences directly above. Here are two examples, with the appropriate punctuation:
The comma is the weakest mark of punctuation; it is, however, an important one.
The comma is the weakest mark of punctuation; it is an important one, however.
Although we usually put the transitional word or phrase squarely between the two clauses, these examples illustrate an inherent difference in how coordinating conjunctions and transitional words function, even when they have the same meaning. Therefore, the differences in punctuation are logical.
A third way of connecting (or separating) independent clauses is to put only a semicolon between them, with no coordinating or transitional word as a link. We usually do this with two "balanced" or closely related clauses, and they are often quite short: Some people like spinach; others don't. We may choose to do this because the coordinating conjunction (in this case, but) is so clearly implied that we don't want to use it. However, we do not (usually) use only a comma in such situations.* We need something stronger. Of course we may have two separate, simple sentences: Some people like spinach. Others don't. We choose the semicolon instead because (since it is not followed by a capital letter) the two related ideas are not separated visually as much as they are by a period and a capital letter. Here are two more examples of the use of only the semicolon between two related complete thoughts:
The dark is not mysterious; it is only dark. [Archibald MacLeish]
Twenty years ago almost nobody had a computer; today millions of people have one.
*Many authorities permit the use of only a comma when the two clauses are very short and very closely related ("Some do, some don't"), but novices – who tend to write too many comma splices anyway – should be wary of doing this.
CONNECTING DEPENDENT (SUBORDINATE) CLAUSES TO THE REST OF THE SENTENCE
Although other kinds of dependent clauses exist, we are concerned here with dependent clauses that are introduced by subordinating conjunctions. Among the words commonly used to introduce a subordinate clause are: after, although, as, because, before, if, once, since, that, though, until, when, whenever, where, wherever, and while. Two-word subordinating conjunctions that are also often used are: even though, as if, and as though.
Perhaps the simplest way to look at subordinate clauses is this: If we take an independent clause (which can stand alone) and put a subordinating conjunction in front of it, we make that independent (standalone) idea dependent. Here's a very simple example:
The phone rang = a complete statement (an independent clause).
When the phone rang or Before the phone rang or any other statement preceded by a subordinating conjunction = an incomplete statement (a dependent clause).
The dependent or subordinate clause may be placed before an independent clause that completes the main thought or after the independent clause that has introduced the main thought. Sentences with this structure (an independent clause + one or more subordinate clauses) are called complex sentences. Here's how it works:
When the phone rang, we were out. (Subordinate clause first)
We were out when the phone rang. (Subordinate clause at end)
The punctuation is not difficult.
> An introductory subordinate clause ends with a comma. Notice that the comma comes at the end of the clause, not after the subordinating conjunction. Another way to look at this is that the comma marks the break between the introductory subordinate clause and the main or independent clause.
> We usually do not put a comma before a subordinate clause that follows the main clause (comes at the end). Some exceptions exist – for example, when we want to emphasize the contrast presented by an ending subordinate clause beginning with although. However, the comma is usually not needed.
Once you understand these principles, you should have little difficulty correctly punctuating compound and complex sentences – i.e., those with two or more clauses. However, you may still make one of the most common errors that students make – the comma splice. If you have not yet done so, go to Avoiding Comma Splices.
Other tips on sentence punctuation are located at Sentence Punctuation: More Pointers.
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