Should you capitalize the word Internet? Web? Earth? Find out why (or why not).
Another word that's sort of like “ground zero,” in that sometimes it's a proper noun and sometimes it's a common noun, is “depression.” If you're talking about a general economic depression, then it's lowercase, but if you're talking about the Great Depression, then you are referring to a specific historical period, so it's capitalized (6).
Planets and heavenly bodies can be tricky. Take the word “earth,” for example. First, when you are using the word “earth” to refer just to dirt, it's lowercase, of course, but when you're talking about our planet, it becomes tricky because there isn't what I consider a strong rule. All the other planet names like Mars and Jupiter are always capitalized because they're names of specific places, but for some reason, most people treat “earth” differently and don't capitalize it.
Sometimes you'll see "earth" capitalized when it's listed with all the other planet names or when it's referred to in an astronomical way. For example, it will likely be capitalized in a sentence about space travel like, “We plan to leave Earth in January and arrive at Mars in October,” but it is likely to be lowercase in a sentence where it is used more generically, like, “I'm wishing for peace on earth and goodwill to men.”
So the word “earth” is an exception to the rule that something is always a proper noun and capitalized if it names one specific place. I hate exceptions, but it's good to know about them.
Since many planets have moons and suns, the words “sun” and “moon” are also almost always lowercase, but like “earth,” you may see them capitalized when they're used in an astronomical sense to repeatedly refer to a specific sun or moon.
History of English Capitalization
I took German in high school, and one of the first things I noticed is that all the nouns are capitalized. Whether they are common nouns or proper nouns, they all get capitalized in German. And I also noticed that some of the kids in my class got confused and started capitalizing all their nouns in English too.
So that's something to guard against if you're studying German. Remember that in English, proper nouns are the only nouns that get capitalized.
Actually, there was a period roughly between 1600 and 1800 when it was trendy to capitalize all nouns in English (7), so if you're reading something written during that time, like the U.S. Constitution, you can also get confused.
And here's a bonus tip from my e-mail newsletter. What about nicknames? Should Mike “The Situation” Sorrentino capitalize his nickname? He should, and he does. In fact, he made sure to note that his nickname should be capitalized when he spelled it while ordering a pizza.
All nicknames are capitalized because they are treated just like names, which makes them proper nouns.
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1. Garner's Modern English Usage. Oxford: Oxford University Press. 2003, p. 392.
2. Saffire, W. The Right Word in the Right Place at the Right Time. Simon and Schuster: New York. 2004.
3. Walsh.B. The Elephants of Style. McGraw-Hill: New York. 2004, p. 40.
4. “Style Update.” Copy Talk. The Canadian Press. April 2003, NO. 177.
5. “Ground Zero,” Yahoo Style Guide. http://styleguide.yahoo.com/word-list/g/ground-zero-ground-zero (accessed September 6, 2010).
6. CliffsNotes.com. Proper Nouns. http://j.mp/bvDKkE (accessed September 9, 2010).
7. Dollinger, S. “What the Capitalization of early Nouns in Canadian English may tell us about 'colonial lag' theory: methods and problems.” Views, 12(1), 2003, p. 24-44. http://j.mp/aXwyWW