English Punctuation

Comma

When to Use a Comma

  • In a series. Use a comma to separate the items in a series of three or more words, phrases or clauses.  
Current job openings include positions in programming, technical writing, advertising and public relations.

Using a comma before the conjunction that joins the last two items in a series to prevent confusion regarding whether the last two items in a series are related.

In the previous example “advertising and public relations” a comma can be not used if the word “relations” refers to “advertising”. If “advertising” has nothing to do with “relations”, a comma should be used to avoid misunderstanding.

 Some more information on comma usage can be found here.
  • To separate independent clauses in a sentence. 

Use a comma to separate independent clauses that are joined by the coordinating conjunctions “and”, “but”, “yet”, “for”, “nor”, and “or.” 

You do not have to back up your files, but doing so is prudent.
  • To separate a subordinate clause or long introductory phrase at the start of a sentence from the main clause. 
Using a text editor, change the last line of the file.
  • After a dependent adverbial clause or prepositional phrase that starts a sentence. 
By recording transactions and automating billing, the financial software saves time and prevents costly errors.
  • To separate an introductory adverb from the rest of the sentence. 
Hopefully, he entered the personnel office.
  • With nonrestrictive phrases. 

Use a comma to set off non-defining relative clauses. 

Writers often refer to this book, which is a style guide for the computer industry.
  • With parenthetic text. 
Use commas to set off short parenthetic material. 

The software, with its simple interface, decreases input time by 50 percent.
  • In addresses. 

Use commas to set off components of an address when the address appears in a sentence or on one line. 

Write to Plirg Systems, Inc., North Bay Village, Florida.
  • In dates. 

Use commas to separate the components of a date. 

She was hired on January 1, 1996, and left six months later.
  • With “for example” and similar expressions. 

Use commas to set off expressions such as “for example,” “that is,” and “namely.” 

Enter the date in MMDDYY format, for example, 110798.
  • The comma should be used between the person's name and the greeting. 

The reason is “direct address”. We use commas to show that we are talking to the reader, not about the reader. 

Hello, Rene.
Danny, thank you for your thoughtful message. 
Congratulations, Michael! 
I hope you know, Donelle, that we appreciate your hard work. 
I am writing to you, Kathryn, with some sad news.

Exception: Do not use a comma with the greeting Dear, as in “Dear Claudio:”, “Dear Claudio,” or “Hi Claudio,”. 

The “Dear Claudio” greeting is shown with both a colon and a comma. The colon is used in formal business emails. The comma is used in less formal ones. 

When Not to Use a Comma

  • When several adjectives are used as a single modifier. This applies to adjectives that describe different qualities of an object, like its color, size, weight, etc. 
Click the small black button at the top of the window.
  • Between two short independent clauses. 
Save your changes and quit the text editor.
  • If a dependent adverbial clause or prepositional phrase appears in its normal order in the sentence. This usually concerns adverbial clauses at the beginning of a sentence.
    Compare these sentences “This feature saves time because it automatically updates system files.” AND “Because this feature automatically updates system files, it saves time.” 
    • In month-year formats. 
    Microsoft introduced Microsoft Windows version 3.0 in May 1990.


    Period

    A period is used to end sentences, just like in Russian, and to designate file extensions. The following rules refer to English and are really noteworthy. 
    • With abbreviations
    A period is used with some abbreviations, and always with those abbreviations that would look like a word otherwise. 

    a.m.
    U.S.
    • In lists
    When a colon introduces a bulleted list, use a period after each entry if it is a complete sentence or a phrase that completes the introduction. 

    The database owner can: 
    • Create and delete a database.
    • Add, delete, or modify a document.
    • Add, delete, or modify any information in the database.

    Do not end the entries with periods if they are all short phrases (three words or fewer). 

    The database includes: 
    • Reports
    • Forms
    • Tables
    • Have a nice weekend. Sincerely, NAME
      In the sentence above there should be a full stop after the words "Have a nice weekend".
      • Mr. vs. Mr 
      British people usually write abbreviations without full stops in modern English. Full stops are normal in American English.

      Mr (AmE Mr.)= Mister, kg (AmE kg.)= kilogram, Ltd = limited (company) 

      Colon 

      A colon looks like this “:”. 

      When to Use a Colon

      • To introduce a list. 
      When introducing a list, use a colon, especially if the introduction contains phrasing such as “the following” or “as follows.”

      The database includes: 
      • Reports
      • Forms
      • Tables
      • Before explanatory text. 
      Use a colon to indicate that the initial clause will be further explained or illustrated by information that follows the colon.
      Note that the colon serves as a substitute for phrases such as “in other words,” “namely,” or “for instance.”
      • After an introduction to a statement or question. 
      Remember this cardinal rule: Never reboot your system until you have saved all of your files.

      When Not to Use a Colon

      • To introduce a figure or a table. 
      The following figure shows the parts of the editing window.
      • In a list that is introduced by “includes” or “are” within a sentence. 
      The base colors that are used in four-color printing are cyan, magenta, yellow, and black.

      Semicolon

      A semicolon looks like this “;”. 

      Avoid using semicolons. Semicolons are often misused and are difficult to read online. Note that it is incorrect to use semicolons at the end of each entry in a list. See rules on Period for more details.