Hyphens - Proposed new version

Hyphens

We discuss here the general principles and CMS style recommendations governing hyphens.

Hyphens should be used to increase clarity, but there is no universally accepted set of hyphenation rules. The trend in scientific writing is to avoid a hyphen when it does not serve a useful purpose, e.g. "pileup", "cross section", "b quark". The recommendations given here are intended for guidance. Authors should feel free to include or omit a hyphen to improve the clarity in any situation, regardless of any rules. Authors should also keep in mind that reorganizing a sentence may be a better way to resolve ambiguities than adding a hyphen.

Hyphenation conventions for commonly used or troublesome terms

Two or more words, unhyphenated

A single word without a hyphen

Hyphenated

Use a hyphen
The following should be hyphenated as attributive adjectives. (An attributive adjective is an adjective that comes before the noun that it is describing or qualifying.)

• A noun + present or past participle: "gas-filled chambers", "English-speaking people", "U-shaped tube".
  Some combinations form passive verb forms, so they must be hyphenated to show they are performing as a unit, e.g. "Doppler-shifted", "Fourier-transformed".

• An adjective + present or past participle: "good-sized sample", "straight-sided cavern", "fine-grained texture"

• "Well", "ill", or "little" + past participle: "well-known theorem", "ill-defined terms", "little-known result".
  Do not hyphenate if the adjective is modified by an adverb: "very well known theorem", "extremely fine grained texture".

• A preposition + noun or adjective: "near-surface reaction", "near-death experience", "next-to-leading-order calculation" (but "calculated to next-to-leading order")

• Temporary compounds formed by an adjective + noun indicating number, dimension, or quality: "single-photon approximation", "three-component gas", "nth-order equation", "low-\pt region".
  

Do NOT use a hyphen
The following combinations should NOT be hyphenated as attributive adjectives.

• An irregular comparative or superlative + participle or noun: "best known result", "least known theorem"

• Foreign phrases: "a priori solution", "in situ technique"

• Adverbs ending in "ly" + adjective or participle: "slowly flowing gas", "highly complex approach", "oppositely charged particles"

• Chemical compounds: "sulfuric acid bath", "carbon dioxide gas", "lead tungstate crystals"

• Compounds indicating direction or placement: "upper right corner", "north central Switzerland"

• Temporary compounds used as attributive adjectives formed by a noun + noun: "energy flow region", "wake surface potential", "jet energy corrections"

• Permanent compounds (frequently used word combinations) that have their own (unhyphenated) dictionary entries: "Higgs boson", "Z boson", "W boson", "top quark", "cross section", "standard model", "black hole", "cosmic ray", "magnetic field", "form factor"

• Other combinations of an adjective + noun that may be considered permanent because of their common usage in our field: "b quark", "b tagging", $\tau$ lepton, "$t$ channel", "$S$ wave"

• Comparative modifiers using "more" or "less" do not need hyphens except on the rare occasions when the meaning is ambiguous without one. For example, "the well read paper", "the less known algorithm".

Usually use a hyphen
The following category of attributive adjectives usually take a hyphen, but some recommendations or journal guidelines will differ.

• Phrases that act as attributive modifiers: "signal-to-noise ratio", "order-of-magnitude estimate", "tag-and-probe procedure"

Always use a hyphen

• Phrases that are listed in the dictionary with hyphens should always use them: "day-to-day variation", "one-to-one correspondence"

Nouns

• Do not hyphenate a noun + gerund or fractions when they act as nouns in a sentence: "problem solving", "data taking", "one half", "two thirds". But do hyphenate them when they are used as an adjective, e.g. "data-taking period", "two-thirds full".

• Use a hyphen with "self" compounds and a verb + preposition (acting as a noun): "self-destruct", "turn-on", "ramp-up"

Words of equal weight
A hyphen is used to connect words of equal weight. Usually, they are connected because they have an "either-or", "from-to", or "between-and" relationship: "wave-particle duality", "argon-ethane gas", "time-space plot", "May-December relationship".

PACS keywords
When specifying the PACS keywords associated with a paper, hyphenate them as they appear in the official listings.

En dashes and em dashes
Use an en dash (a double hyphen -- in LaTeX, with no spaces) to indicate a range of values, e.g. "5--10", or something attributed to two people, e.g. "Bose--Einstein correlations". Use an em dash (a triple hyphen --- in LaTeX, with no spaces) for an article of punctuation, e.g. "The measurement failed---we messed it up."

Two related hyphenated words near each other
If you have two related hyphenated words near each other in a sentence, you can shorten the first hyphenated word by omitting the hyphenated part and leaving a hyphen at the end of it. Example: "Both initial- and final-state radiation are taken into account."