Do 'However' and 'So' Need Commas?


Every Wednesday, Editing for Grammarphobes 2.0 features handy tips to enhance all of our writing, from daily emails to articles to books. After all, everyone needs to write, right?

Image courtesy of Grammarly.

Today’s topic comes from an email I received from a reader.

Hello Karen,

I have some questions about comma usage that I was hoping you could answer in one of your posts. How should we use commas for the following?

* Single and multiple, sentence-leading, prepositional phrases.

* Comma usage when “so” is anywhere within a sentence.

* Comma usage when “however” is anywhere within a sentence.

Thanks for your help.


Let’s answer these one at a time.

Prepositional Phrases

First, commas should be used after a prepositional phrase at the beginning of a sentence, such as in the example below.


By the time I arrived, all the guests were gone.

Grammar Girl suggests “the longer the prepositional phrase, the more you need the comma.” Chicago Manual of Style (CMS) agrees, noting that introductory adverbial phrases can be followed by commas, but they’re not always necessary unless misreading is likely.  I prefer to always use the commas after introductory prepositional phrases for clarity.


By noon, the rain let up. 

Of course, you also could structure the sentence a different way to avoid starting with a prepositional phrase altogether, like in the following examples.


All the guests were gone by the time I arrived.

The rain let up by noon.

It depends what you prefer, but both are grammatically correct. Sometimes starting a sentence with a prepositional phrase varies the sentence flow and emphasizes a particular sentence, which comes in handy, especially in writing fiction.

'So' in the Middle

Regarding so in the middle of a sentence, the rule is to use a comma before any coordinating conjunction, including so, and, but, nor, for, and or.


It’s raining, so I grabbed my umbrella.

The Green Bay Packers lost to the Detroit Lions, so I was happy.

'So' in the Beginning

But be warned. Using so to begin a sentence can be a little too colloquial for some kinds of writing. Best to know your audience. If you’re writing for a corporate setting, it might be better to omit so and go straight into the sentence. For more casual pieces, a sentence like the one below can be perfectly acceptable.


So, what’s for dinner?

Using 'However'

Regarding however, the usual rule is to use commas after introductory adverbs. Most agree that however and so also fit into this category.


However, I disagree.

So, what’s next?

CMS states that “however has been used as a conjunctive adverb since the fourteenth century.” It is more “ponderous” and has “less impact than the simple but,” CMS notes, and it is “more effectively used within a sentence to emphasize the word or phrase that precedes it.” When placed in the middle of a sentence, however should be set off by commas.

The publication offer the following example.

“The job seemed exciting at first. Soon, however, it turned out to be exceedingly dull.”

I hope that answers your question, David. Thanks so much for writing in.

If you have a grammar question, drop me a line at, and I’ll answer it here.

Please join me next week when we tackle abbreviations, including etc., et al, and eg. What do they mean? When should they be used?

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These books are on my desk at all times. Maybe they'll help you as well.

The Associated Press Stylebook, 2017 edition

The Chicago Manual of Style, 17th edition
Strunk and White's The Elements of Style


A professional writer/editor for almost 30 years, Karen Wojcik Berner's wide and varied experience includes such topics as grammar, blog content, book reviews, corporate communications, the arts, paint and coatings, real estate, the fire service, writing and literature, research, and publishing. An award-winning journalist, her work has appeared in several magazines, newspapers, and blogs, including the Chicago Tribune, Writer Unboxed, Women's Fiction Writers, Naperville magazine, and Fresh Fiction. She also is the author of the Bibliophiles series, contemporary fiction with a sprinkling of the classics, and is a member of the Chicago Writers’ Association. For more information on Karen, please visit


Great post! I love commas. They are my favorite form of punctuation. I'm such a grammar nerd. ;)

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