To Link Spelled-Out Numbers

A hyphen joins spelled-out numbers from 21 through 99 and spelled-out fractions:

twenty-one moving parts

the thirty-third experiment

four-fifths of the subjects

To Divide Words

In general, words are not divided in scientific writing. However, if necessary, hyphens are used to split words at the end of a line to prevent large spaces between words in justified text and noticeably uneven margins in unjustified text.

To Stand for to or through Between Letters and Numbers

Hyphens stand for through or to, especially in bibliographies and reference lists. However, when a number, letter, or date is preceded by the word from, the word to is used instead of a hyphen:

pages 25-63

sections 15.2-15.8

1901-1911

from 1901 to 1911

Specialized Uses

A hyphen is used in the following circumstances:

- to represent single bonds in chemical formulas:

(CH₃)₂-CH-CH₂-CH(NH₂)-OH

- between the spelled-out name of a chemical element and the mass number of the specific isotope:

carbon-14

- between sequences of amino acids:

Asp-His-Lys

Suspended Hyphens

If all unit modifiers in a series end with the same term, the term does not have to be repeated each time; for brevity you may suspend the hyphens and use the modified term only at the end of the series:

The first-order, second-order, and third-order equations have all been solved.

The first-, second-, and third-order equations have all been solved.

2- and 3-phase controllers

The rules below describe some other situations where a hyphen should not be used:

One should not hyphenate Latin expressions or non-English-language phrases used in an adjectival sense, e.g., in vivo experiments, an a priori argument, postmortem findings. In the text, hyphens are not used to express a range (e.g., 10% to 20% of the substance), except if the range expresses fiscal years or life spans (e.g., the 2003-2005 data set) or if the range is given in parentheses (mean age was 22 years; [range, 11-32 years]). One should not hyphenate modifiers in which the second element is a number or letter, e.g., Type II diabetes, Grade A material.

3.13 Dashes

Dashes are used sparingly to indicate abrupt shifts in thought and to set off or emphasize appositional or parenthetical elements or interjections. You can use a dash in the same way as round brackets to add extra, less important information. The dash, however, is somewhat informal, so it is not so often used in scientific reports as commas or brackets:

Although we have made these comments with specific reference to water--only because of our familiarity with water--all pure substances exhibit the same behavior.

In typewritten documents, two hyphens (--) may be used with no spaces between or around them to form a dash.

The Table shows the four types of dashes that differ in length. The en dash is longer than a hyphen but is half the length of the em dash:

Name of Dash	Symbol	Appropriate Use
en dash	–	The en dash shows relational distinction in a hyphenated or compound modifier if one element consists of two words or a hyphenated word, or when the word being modified is a compound. Multiple sclerosis–like symptoms, Krebs-Henseleit–bufered solution, post–World War II, non–English-language journals
em dash	—	Not used in scientific writing because it indicates a sudden interruption or break in thought (Punctuation Marks Indicating Emotion).
2-em dash	——	Not used in scientific writing.
3-em dash	———	Not used in scientific writing.