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I always get confused when using hyphenated words in my research papers. Is there any specific rule for using hyphenated words? For example, which one of the following is the correct usage of co scheduling? One has smallcase s, while the other one has uppercase s. Is it just simply a taste of the writer? Google shows both the words along with coscheduling.

Co-scheduling or Co-Scheduling

Moreover, wikipedia tells that:

Certain prefixes (co-, pre-, mid-, de-, non-, anti-, etc.) may or may not be hyphenated.

Could someone clarify this?

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up vote 2 down vote accepted

The problem here is that there is not one true answer. Google will display the various styles used, but there is not one correct one.

To determine the style that you should should use, do the following.

Look up the word in the standard dictionary you are supposed to use. (If there isn't a standard dictionary for your project, choose one). If the word is in the dictionary, use that spelling. If not, look up the hyphenation rules in the style manual you are supposed to use. (If there isn't a standard style manual for your project, choose one). Hyphenate the word according to those rules.

For questions of capitalization, you'll have to refer once again to the style manual. It should contain rules for capitalizing hyphenated words. But be aware, the capitalization rule for a hyphenated word in a title may differ from that at the beginning of a sentence.


Let's use your word, "co scheduling", and the rules from the Penn State Editorial Style Manual.

The manual specifies "Webster’s Collegiate Dictionary, current edition" for spelling and hyphenation. In that dictionary there is no entry for a word co that would properly modify scheduling, which means that "co scheduling" is incorrect. There are also no entries for either co-scheduling or coscheduling, so we can't follow the dictionary's spelling.

There are entries for the prefix co- and the word scheduling. So the word must be formed by merging these two. We need to use the style manual to determine how to do that. The section on hyphens states: "Words formed with the prefix co should be hyphenated." So if you follow Penn State's rules, the word should be co-scheduling.

The Penn State manual is silent on the rules for capitalizing hyphenated words and refers users to the Chicago Manual of Style in that case. That manual states: "Do not capitalize the second element if (a) it is a participle modifying the first element or (b) both elements constitute a single word." Because co- is a prefix, that means co-scheduling is a single word, and therefore the capitalized form is Co-scheduling.

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It's perfectly acceptable to capitalize both parts of a hyphenated word in a title: e.g.: "A Method of Co-Scheduling", and my impression is that it is actually more common. See this question. If you're capitalizing it at the beginning of a sentence, then you write "Co-scheduling ...". – Peter Shor Sep 10 '11 at 23:11
It may be acceptable to use "Co-Scheduling" -- but it is not acceptable everywhere, including Penn State. The answer from the question you reference begins: "Capitalization of hyphenated words in general is really more a question of style than anything else." In my answer I tried to show how to apply a set of style rules, specifically Penn State's, to the original question. If I had chosen a different set, the result might have been "Co-Scheduling" for titles. This is not really about acceptable or unacceptable -- it's about consistency. – D Krueger Sep 11 '11 at 4:34

Wikipedia's statement is accurate, but not very specific. Many of those prefixes have some more specific rules that govern their use:

Rule 1. The current trend is to do away with unnecessary hyphens. Therefore, attach most prefixes and suffixes onto root words without a hyphen. Examples: noncompliance, copayment, semiconscious, fortyish

Rule 2. Hyphenate prefixes when they come before proper nouns. Example: un-American

Rule 3. Hyphenate prefixes ending in an a or i only when the root word begins with the same letter. Examples: ultra-ambitious, semi-invalid

Rule 4. When a prefix ends in one vowel and a root word begins with a different vowel, generally attach them without a hyphen. Examples: antiaircraft, proactive

Rule 5. Prefixes and root words that result in double e's and double o's are usually combined to form one word. Examples: preemployment, coordinate Exceptions: de-emphasize, co-owner

Rule 6. Hyphenate all words beginning with self except for selfish and selfless. Examples: self-assured, self-respect, self-addressed

Rule 7. Use a hyphen with the prefix ex. Example: His ex-wife sued for nonsupport.

Rule 8. Use the hyphen with the prefix re only when:

  • the re means again AND omitting the hyphen would cause confusion with another word. Examples: Will she recover from her illness?
  • Re does not mean again. (I have re-covered the sofa twice.)
  • Re does mean again AND omitting the hyphen would have caused confusion with another word. (The stamps have been reissued.)
  • Re means again but would not cause confusion with another word. (I must re-press the shirt.)
  • Re means again AND omitting the hyphen would have caused confusion with another word.
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Certain prefixes (co-, pre-, mid-, de-, non-, anti-, etc.) may or may not be hyphenated.

The rule is generally that terms start off as hyphenated and then as they become more commonly used gradually drop the hyphen. Unless the unhyphenated version looks confusing or difficult to pronounce.

For example electronic mail became e-mail then email.

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