Using a Comma after an Adverbial Clause or Phrase
at the Start of Sentence
 
When words which "set the scene" for the main part of the sentence appear at the front of the sentence, it is usual to offset them with a comma. For example:

  • At 4 o'clock, I'll jump in the river.
  • As I know the ground, I'll go first.
  • Under the water, you can see the swans' legs going hell for leather.
(NB: These "scene setting" words of introduction are called adverbial clauses or phrases.)

When the introduction is just one word (e.g., Yesterday, Here, Now), it is common practice to omit the comma.
 

Using a Comma after an Introductory Adverbial Clause or Phrase

It is common for a sentence to start with an introduction. An introduction can be anything from just one word to a long clause.

An introduction is used to state a time, a place, a condition, a frequency, or a fact before the main part of the sentence.

(These "introductions" vary hugely. They are known as dependent clauses because they cannot stand alone as complete ideas. If an "introduction" contains its own subject and verb, it will be an adverbial clause, otherwise it will be an adverbial phrase. The main part of the sentence (i.e., the clause after the "introduction") is called an independent clause.)

Read more about clauses and phrases.

Examples of Introductory Adverbial Clauses and Phrases

In these examples, the introductory adverbial clauses and phrases are shaded:

  • In the centre of London, the number of people who fell victim to pickpockets rose by 30 per cent in a month.
  • (This adverbial phrase sets a place.)

  • After twelve years of therapy, my psychiatrist said something that brought tears to my eyes. He said, "No hablo ingles."
  • (This adverbial phrase sets a time.)

  • In ancient Rome, it was considered a sign of leadership to be born with a crooked nose.
  • (This adverbial phrase sets a place and a time.)

  • As soon as the cake is golden-brown, take it out of the oven.
  • (This adverbial clause sets a time.)

  • From the moment I picked your book up until I laid it down, I was convulsed with laughter. Someday, I intend reading it. (Groucho Marx)
  • (The first is an adverbial phrase that sets a time. The second is an adverbial phrase that sets a time.)

  • When I was young, I used to think that money was the most important thing in life. Now that I am old, I know it is. (Oscar Wilde)
  • (Both adverbial clauses set a time.)

  • On Tuesday 4th July a band played carols in the park for 8 hours.
  • (The adverbial phrase On Tuesday 4th July sets a time. It is an introduction and should be followed by a comma.)

  • Having spoken to John, I can confirm that the meeting is definitely off.
  • (The phrase Having spoken to John states a fact that "sets the scene." This type of phrase is known as a participle phrase.)

  • As you are well aware, the latest figures do not look promising.
  • (The adverbial clause As you are well aware states a fact that "sets the scene.")

  • After the secretary had read the minutes of the meeting, the chairman asked for the financial report.
  • (The adverbial clause After the secretary had read the minutes of the meeting sets a time.)

  • A band played in the park for 8 hours on Tuesday 4th July.
  • (The adverbial phrase on Tuesday 4th July sets a time, but it is not an introduction. It is at the back end of the sentence. Therefore, no comma is required.)

  • On Tuesday 4th July, a band played in the park for 8 hours.
  • (Compare this example to the one above.)

  • If you are going through hell, keep going. (Winston Churchill)
  • (This adverbial clause sets a condition.)
 
ONLY USE A COMMA FOR AN INTRODUCTION 

Words that "set the scene" do not always start the sentence; they could appear at the back or in the middle. A comma is only expected when these words appear at the front of the sentence. This is very handy to know. Look the examples below:

  • At 4 o'clock, the new manager, David Bain, will visit.
  • (This is correct, but it has too many commas. It's messy.)

  • The new manager, David Bain, will visit at 4 o'clock.
  • (This is much tidier.)
Here is an example in the middle of a sentence:

  • I'm very proud of my gold pocket watch. My grandfather, on his deathbed, sold me this watch. (Woody Allen)
Commas have been used in the example above, but they were not necessary because the phrase that sets the scene appears in the middle not at the beginning.

A LOT OF LENIENCY ON THIS RULING

Regardless of where the scene-setting words appear (start, middle or end), there is some leniency on whether to use a comma or not. The primary purpose of a comma (or commas if it appears in the middle) is to aid your reader. Above all else, making your text easy to read should determine whether you use a comma or not.

Note: When the introduction is a participle phrase describing the subject of the sentence, you must separate the participle phrase and the subject with a comma. For example:

  • Having read your concerns, Prof. Jones has agreed to meet with you.
  • (In this example, Having read your concerns is the participle phrase, and Prof. Jones is the subject. The comma is required.)
IT'S OKAY TO DROP THE COMMA AFTER A ONE-WORD "INTRODUCTION"

Most of the scene-setting words are classified as adverbs. When they are made up of more than one word, they are called adverbial phrases or clauses. When they're just one word, it is a common practice to drop the comma. For example:

  • The day before yesterday, I caught another 10lb bass.
  • (A comma is expected after an introductory adverbial phrase.)
  • Yesterday I caught another 10lb bass.
  • (A comma after Yesterday would look a bit unwieldy, so it's okay to omit it.)
 

See also:

Commas after a transitional phrase
Commas after interjections (yes, no, indeed)
Commas before conjunctions (and, or, but)
Commas for parenthesis
Commas in lists
Commas with a long subject
Commas with numbers
Commas with quotation (speech) marks
Commas with the vocative case
Commas with Dear, Hello, and Hi
List of easily confused words