Author and journalist Joan Didion once said: "Grammar is a piano I play by ear. All I know about grammar is its power." Grammar clarifies communication and gives credibility to the writer -- so while it's necessary to follow the rules, it's also necessary to fine tune your rules to each situation and audience to guarantee clarity.

Via this column, we'll explore one grammar rule each week. If you have a grammar question you'd like me to address, please drop me a line at grace.lavigne@prnewswire.com and I'll do my best to answer it.

Today we'll address the rules of capitalization. We all (hopefully) know that we should capitalize proper nouns (which are one-of-a-kind words like New Jersey or Barack Obama), but sometimes the rules of capitalization in more specific environments can get a little fuzzy. Here are some frequent mistakes:

Nouns that can be proper or common, like the "earth" vs. "Earth":

• The earth smells like rain and roses. (earth = dirt, ground)
• The Earth looks beautiful from space. (Earth = specific planet)
• I live in a white house, but I don't live in the White House (I only wish I did).

Capitalize a person's title when it precedes their name, but do not capitalize the title if it's acting as a description following the name:

• President Barack Obama was inaugurated in 2009. / Barack Obama, president of the United States, was inaugurated in 2009.
• ProfNet Editor Jason Hahn reads queries. / Jason Hahn, ProfNet editor, reads queries. (ProfNet remains capitalized because it's a proper noun.)
• CEO Larry Page founded Google. / Larry Page, CEO, founded Google. (CEO remains capitalized because it's an acronym.)

Is it "mom and dad" or "Mom and Dad"?

• Mom and Dad are going to be so mad.
• My mom and dad are going to be so mad.

The trick here is to replace "Mom and Dad" or "mom and dad" with names:

• George and Lynne are going to be so mad. (Correct)
• My George and Lynne are going to be so mad. (Wrong -- therefore "mom and dad" would not be capitalized)

Names of holidays are capitalized, but the word "holiday" is not:

• Halloween is my favorite holiday because I love to scare people.

Months and days of the week are capitalized, but seasons are not:

• My favorite season is fall. My favorite month is October.
• I love Saturdays in the summer! (Who doesn't?)

Diseases are not capitalized unless there is a person associated with the name:

• My grandmother has Alzheimer's disease. (named after Alois Alzheimer)
• She has arthritis and diabetes.
• I don't want to get pancreatic cancer.

Compass directions are always lowercase; regions are always uppercases:

• We're headed east to my house. (direction)
• My house is in the East. (region)

Lowercase academic subjects, unless referring to a specific class or a class associated with a language:

• I love math. (general subject)
• I loathe History 101. (specific class)
• I major in English. (associated with a language)

Degrees are lowercase too, unless they are formal names:

• I received my master's degree in 2009. (general reference)
• I received my Master of Arts in 2009. (specific name of the degree)
• I received my M.A. in 2009. (acronym)