Errors with commas are the most common type of punctuation mistake. Nine out of ten documents we edit are littered with comma-related errors.1 This article outlines five ways in which commas are included in error.

Comma before that

This error occurs when a sentence has an offset clause. An offset clause is  a clause that is an aside, one that can be removed and the sentence still reads correctly. Unless they are short, offset clauses should be marked off with commas. A frequent error is to include the comma but misplace it.

🗴  Rodríguez knew, that to pass the examination with flying colours, his language had to be flawless.

The offset clause here is
to pass the examination with flying colours
and not
that to pass the examination with flying colours.

This error is made surprisingly often. It is as if the writer knows a comma is needed (presumably because one is often seen near that) but he or she is ignorant of its purpose. The sentence should read:

✓  Rodriguez knew that, to pass the examination with flying colours, his language had to be flawless.

More examples:

🗴  On a bright sunny morning, John was disconcerted, when on trying to understand Einstein’s Theory of Relatively, his head exploded.

In that example, if you remove the phrase in commas, the resulting sentence is grammatically flawed, because you get this:

🗴  On a bright sunny morning, John was disconcerted his head exploded.

No, rather the comma must go after when:

✓  On a bright sunny morning, John was disconcerted when, on trying to understand Einstein’s Theory of Relatively, his head exploded.

Comma separating list items

When listing two items, do not separate the items with a comma.

🗴  Black holes inspire awe, and wonder.

In the above example, the comma separating the items awe and wonder serves no purpose and has no business being there.

That should be clear. However, as is often the case, wordiness is confusing. Consider:

🗴  In Wave 1, 77% of households said they had enough food, and in Wave 2, it was 85%.

In this case, the list is still just two items, separated by and. However, the writer appears to have become muddled by the offset phrase in Wave 2, which needs to be offset with commas. He has used a comma but misplaced it. This is how it should be written:

✓  In Wave 1, 77% of households said they had enough food and, in Wave 2, it was 85%.

Why the insistence here on lists of just two items? Because, with three or more items, a comma can be used. This is called the Oxford comma and is a cause of disagreement among the cognoscente. However, that is a topic for another time.
The Oxford comma in use:

✓  Black holes inspire awe, wonder, and a sense of our insignificance.

Comma before a verb

Do not separate a verb and its subject with a comma. You would not write the following:

🗴  Nobel, invented dynamite.

It is obvious that sentence should have no comma. If you are not sure, try reading aloud. If you do not pause for the comma or the pause feels wrong, the comma is probably in error. You would not read that as:

🗴  Nobel [pause] invented dynamite.

Yes, you could pause, but you would do so for some unusual effect.

Do not be fooled by a mere multitude of words being the subject of a verb.

🗴  The reason Anna opted to consult Ezra, was a passion for improving her writing skills.
✓  The reason Anna opted to consult Ezra was a passion for improving her writing skills.

It seems that the longer the subject of the verb the more writers think a comma is needed. Consider:

🗴  The number of interviewees, location and setting, distance between interviewer and interviewee, and frequency of interviews conducted in the fieldwork period, influence the outcome.

That last comma is in error. That should be:

✓  The number of interviewees, location and setting, distance between interviewer and interviewee, and frequency of interviews conducted in the fieldwork period influence the outcome.

Another example:

🗴  Workers who perform their work tasks from home, have permanent employment contracts.
✓  Workers who perform their work tasks from home have permanent employment contracts.

A final note: do not be deceived by a bracket.

🗴  The European Union (EU), was founded in 1993.
✓  The European Union (EU) was founded in 1993.

Run-on sentences

Many grammar guides address run-on sentences, so they are only touched on here. Run-on sentences occur when grammatically complete sentences are joinedr with a comma (or no punctuation at all).

🗴  The hypothesis is confirmed, Einstein was a genius.
🗴  The hypothesis is confirmed Einstein was a genius.

In these examples, the two sentences need to be correctly joined or separated into separate sentences.

✓  The hypothesis is confirmed; Einstein was a genius. [semicolon used]
✓  The hypothesis is confirmed. Einstein was a genius. [two sentences used]

Comma after includes

With lists, no comma goes after includes.

🗴  Ezra includes, style checks, an acronym analysis, and a paragraph-length analysis.

It would be better to put a colon after includes but even that is poor style. You need no punctuation at all.

✓  Ezra includes style checks, an acronym analysis, and a paragraph-length analysis.

Medical comma

After the serious stuff, something to put a smile on your face. From a medical student’s exam paper:

“Diabetic comma is a serious sign.”2

What a difference one letter makes!

Notes and references

  1. This is rough estimate for the purposes of illustration and not a measured value.
  2. Dim Wit by Rosemarie Jarski, Ebury Press, UK, 2008, p. 66.