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I was looking back through my grammar posts the other day when I made a rather startling discovery: in all my years of writing this blog, I had somehow neglected to write a piece covering the two major causes of comma splices.

I suspect that because I’ve given this explanation in a total of five books now, I took it for granted that I had covered both issues  in a single post, back in… oh, I don’t know… 2012 maybe? But apparently not.

Since this is among the most frequently tested concepts on the SAT and the ACT, an occasional target of questions on the GMAT, and a HUGELY common error in IELTS essays, I would count this omission among the greatest oversights in Critical Reader history.

So here goes.

First, the very basics: As most people know, a period (i.e., full stop) is used to separate two complete sentences from one another. As fewer people know, a semicolon can also be used instead.

A comma, however, is not the grammatical equivalent of these punctuation marks, and so it cannot be placed between two full sentences. When this rule is broken, the result is known as a comma splice. For the purposes of any standardized test you might take, comma splices are always wrong.

Now, in principle comma splices can involve any number of sentence types and patterns, but in reality they mostly occur in two very specific constructions. We’re going to consider them one at a time.

 

1)  Pronoun as Subject

Look at the following sentences:

 

Sentence 1: E-commerce has provided many new opportunities for companies as well as consumers.

Sentence 2: It has provided many new opportunities for companies as well as consumers.

 

Notice that Sentence 1 uses a noun as its subject (e-commerce), whereas Sentence 2 uses a pronoun (it).

Taken out of context, Sentence 2 does not make sense—it does not tell us what has provided new opportunities. As a result, many people incorrectly assume that it cannot be a sentence.

But here’s the rule: changing the noun to a pronoun has no grammatical effect. A sentence whose subject is a noun and a sentence whose subject is a pronoun are grammatically identical; they must both follow a period/full stop or a semicolon, not a comma. It does not matter whether the “pronoun” version is meaningful as an independent statement.

 

Correct: Over the last several decades, e-commerce has become an increasingly popular mode of conducting business. It has provided many new opportunities for retailers as well as consumers.

 

Incorrect: Over the last several decades, e-commerce has become an increasingly popular mode of conducting business, it has provided many new opportunities for retailers as well as consumers.

 

Also, this should go without saying, but because I have actually read a number of essays punctuated this way, I feel obligated to point out that you should never, ever do this:

 

Incorrect: Over the last several decades, e-commerce has become an increasingly popular mode of conducting business, It has provided many new opportunities for retailers as well as consumers.

 

Or even worse, this:

 

Incorrect: Over the last several decades, e-commerce has become an increasingly popular mode of conducting business,It has provided many new opportunities for retailers as well as consumers.

 

From what I’ve observed over the years, comma splices typically involve it, he, she, or they; however, you should keep in mind that all of the following types of pronouns can serve as subjects:

 

Subject pronouns: I, you, s/he, it, we, they 

Possessive pronouns: mine, yours, his/hers, ours, theirs 

Demonstrative pronouns: this, that, these, those 

 

 

2) Conjunctive Adverb Begins a Clause

Conjunctive adverbs are transitional words and phrases (linking devices) that can be placed at the beginning of an independent clause (always followed by a comma). Common examples include:

Now, compare these two sentences:

 

Sentence 1: Customers have fewer opportunities to inspect goods directly before making a purchase.

Sentence 2: However, customers have fewer opportunities to inspect goods directly before making a purchase.

 

Notice that the first version begins with a noun (the subject, customers), whereas the second version begins with the conjunctive adverb however. But guess what: grammatically, these statements are identical. They are both complete sentences, and they must both follow a period or semicolon.

 

Correct: E-commerce offers many advantages in terms of convenience, affordability and choice. However, customers have fewer opportunities to inspect goods directly before they make a purchase.

 

Correct: E-commerce offers many advantages in terms of convenience, affordability and choice; however, customers have fewer opportunities to inspect goods directly before they make a purchase.

 

BUT

 

Incorrect: E-commerce offers many advantages in terms of convenience, affordability and choice, however, customers have fewer opportunities to inspect goods directly before they make a purchase.

 

It does not matter how many sentences you see written like the one above; that construction is still wrong.

 

Note that adverb-based comma splices can also involve adverbs of time, e.g., today, yesterday, still. Again, placing one of these words at the beginning of a sentence has no grammatical effect.

 

Correct: In the past, consumer had no choice but to make all of their purchases in physical stores. Today, they can choose from among an endless assortment of items online.

 

Incorrect: In the past, consumer had no choice but to make all of their purchases in physical stores, today, they can choose from among an endless assortment of items online.

 

So there you have it: For all practical purposes, everything you need to know about this often-abused area of English punctuation in one short post. You just have to remember to apply what you’ve learned. But don’t worry: you’ll have endless opportunities to practice. That’s pretty much a guarantee.