Using the wrong style of punctuation in the wrong context can cost you a job interview or credibility among your coworkers and peers. When you use correct punctuation in the right context, it signals that you have an eye for detail, care about professionalism and are capable of communicating effectively. There are two types of punctuation that are used in different contexts: open punctuation and closed punctuation. Knowing how and when to use each of these styles will prove useful in your personal and professional life.

Open Punctuation

Open punctuation uses fewer terminal punctuation marks -- periods and other marks that denote the end of a sentence -- as well as fewer commas than closed punctuation. When you think of open punctuation, “minimalism” is the name of the game. When using open style, don’t use periods in abbreviations, acronyms or times of day. Avoid using commas where one is optional in a sentence, such as the Oxford comma -- the comma before the conjunction in a list. When in doubt, remove the comma.

When to Use

Most commonly, open punctuation is used for business and cover letters, but only when it is specifically indicated that open style is preferred. When writing such a letter, don't include commas in any of the addresses, dates or titles of individuals. Omit the comma after the salutary greeting -- as in “To Whom It May Concern” -- with no comma or colon afterward. If you're writing a business or cover letter in open style, use block style -- don't indent any of your paragraphs, but rather, your text should be left-justified.

Open Punctuation Examples

When writing in open punctuation style, omit periods and commas in several places where it may seem counterintuitive. Remember that when using open punctuation, you do not use punctuation in times of day or dates. Don't use periods in "am" or "pm." Don't use periods or commas in nicknames, addresses or a person's title. For example, you would say, "AJ Green PhD" instead of "A.J. Green, Ph.D." When writing an address in an open style letterhead you would do so as follows:

Applegrove Business LLC PO Box 58 SPRINGFIELD

Closed Punctuation

In contrast to open punctuation, closed punctuation uses commas and periods in a strict manner. Closed punctuation is what you’d typically learn and use in an English classroom. With abbreviations, introductory greetings or a letter closing, you use commas and periods. For example, when you write “Dear Mr. Jones,” or sign a letter “Sincerely,” you’d use a comma after both phrases, as opposed to open punctuation.

When to Use

Closed punctuation is used in everyday situations, scholarly writing and business writing, unless a posting or business specifically asks for letters to be written in open punctuation. When using closed punctuation, use periods in times of day such as "a.m." Use periods in abbreviations of degrees, a person's title or degree and when using acronyms. For example, you would use periods in instances such as "Ph.D." and "P.O. Box."

Closed Punctuation Examples

In contrast to open punctuation, closed punctuation calls for an abundance of periods and commas. When you denote times of day, use periods in "a.m." and "p.m." Likewise, when referring to nicknames, titles and degrees, use periods and commas. For example, you would say "A.J. Green, Ph.D." and not "AJ Green PhD." It's the exact opposite of open punctuation style. When writing an address for a letterhead, you would do so as follows:

Applegrove Business, LLC P.O. Box 58 SPRINGFIELD.