Therefore and Too are conjunctive adverbs, and they cause a lot of problems with commas. Before we look at using commas with therefore and too, we need to understand conjunctive adverbs and what they do.
What Conjunctive Adverbs Do
A conjunctive adverb shows how the idea in one sentence or independent clause is related, or connected, to the idea in the previous sentence or independent clause. Conjunctive adverbs include such words as additionally, finally, however, indeed, in fact, rather, similarly, therefore, thus, and too.
Let’s look at an example to see how conjunctive adverbs affect meaning.
She left early. Therefore, he was lonely.
She left early. He was lonely.
In the first example, we know that her early departure caused his loneliness. Therefore indicates a cause and effect relationship between the two sentences. The conjunctive adverb connects the idea in sentence two to the idea in sentence one. It indicates how he was lonely relates to She left early.
Without the conjunctive adverb (second example), the two sentences present two unrelated ideas. What does his loneliness have to do with her early departure. In the second example, nothing.
Commas with Conjunctive Adverbs
When the conjunctive adverb is at the beginning of the first example, it needs to be followed by a comma to separate it from the rest of the sentence (Zen Comma Rule N). Let’s look at another example sentence.
The town flooded; as such, the field is unusable.
In this example, the conjunctive adverb as such is the first word of the second independent clause. (Notice the semicolon that joins the two clauses.) It is also followed by a comma to separate it from the information that follows it.
These examples demonstrate the most common placement for the conjunctive adverbs: at the beginning of the sentence. However, like all adverbs, conjunctive adverbs can be moved to various locations in an independent clause, as in the next example.
I, too, am ready for dinner.
This example, with too inside the sentence, demonstrates how the conjunctive adverb can be placed within the sentence. This sample also follows the rule for commas with conjunctive adverbs. It uses commas with too. The conjunctive adverb too is separated from the rest of the sentence with commas before and after it.
Too at the End of the Sentence
The comma with the word too causes a lot of confusion when too is used at the end of a sentence. If you put too at the end of the sentence, it will still need to be separated from the rest of the sentence with a comma.
Some style guides state that the comma is optional when too is the last word. Others say it is required because it follows the rule about separating conjunctive adverbs with commas. However, optional isn’t the same thing as wrong, which means your safest strategy is always to use it. The sentence won’t be considered wrong if you use the comma, but you may be criticized if you leave it out. (This is why I recommend always using optional commas.)
Too Many Commas!
When we follow the rule about using commas with conjunctive adverbs, especially with too, we can create sentences with a lot of commas. For example, we might have a sentence like this one:
Therefore, he, too, will go.
This use of commas, perhaps more than any other use, can create sentences that sound choppy. Each comma creates a slight pause, so when you put commas around internal conjunctive adverbs, you may end up with a sentence that has many pauses.
This example contains only five words, but it also contains three commas. It has a comma after nearly every word. That’s a lot of commas! It looks overly complicated, and it will sound choppy if you read it aloud.
My advice in situations like this is to revise the sentence. You can find a different way to express your idea, re-order the words, or leave out the conjunctive adverb if it is not necessary. For example, you can revise the sentence as follows.
Therefore, he will go.
In this revision, too is implied by the sentence. This is a much nicer, more economic, and smoother-sounding sentence.
Need help with commas? Get Zen Comma, an instructive reference guide on the 17 major uses and misuses of commas, available in PDF and Kindle formats. Read more about Zen Comma.