Some compound words are written without hyphens (nonaggression, nonbeliever), some with hyphens (well-intentioned), and others with spaces (post office).

Is there a rule or good guide as to which option should be used?

  • Related.
    – tchrist
    Commented Jun 15 at 19:47
  • @tchrist That question asks about run versus ran.
    – apaderno
    Commented Jun 15 at 21:01
  • Ooops, I'll have mispasted the wrong link; thanks for noticing.
    – tchrist
    Commented Jun 16 at 11:57
  • @tchrist I was just wondering in which way that question was related. For a moment, I thought it was because a comment that suggested a compound word. 😉
    – apaderno
    Commented Jun 16 at 15:43
  • 1
    Oh yes, that must have been what I was thinking, that it should be pasture-run sheep, like student-run newspapers or air-breathing fish or fear-driven desperation or sun-blessed vineyards or bottle-fed kittens.
    – tchrist
    Commented Jun 16 at 16:16

7 Answers 7


In English, there are three types of compound words:

  1. the closed form, in which the words are melded together, such as firefly, secondhand, softball, childlike, crosstown, redhead, keyboard, makeup, notebook;

  2. the hyphenated form, such as daughter-in-law, master-at-arms, over-the-counter, six-pack, six-year-old, mass-produced;

  3. and the open form, such as post office, real estate, middle class, full moon, half sister, attorney general.

For the most part, compound words that are created by adding a prefix are not hyphenated. For example, there are the words anteroom, extraordinary and coordinate. Some exceptions to this rule are (from the link above):

  1. compounds in which the second element is capitalized or a number: anti-Semitic, pre-1998, post-Freudian
  2. compounds which need hyphens to avoid confusion: un-ionized (as distinguished from unionized), co-op
  3. compounds in which a vowel would be repeated (especially to avoid confusion): co-op, semi-independent, anti-intellectual (but reestablish, reedit)
  4. compounds consisting of more than one word: (poster's note: these are phrasal adjectives) non-English-speaking, pre-Civil War
  5. compounds that would be difficult to read without a hyphen: pro-life, pro-choice, co-edited

Your original example of "well-intentioned" is also explained here:

The other time we must use hyphenation is to join a word to a past participle to create a single adjective preceding the noun it modifies: "a well-intentioned plan," for example, or "a horseshoe-shaped bar."

So, why isn't nonaggression hyphenated? It can be broken into non + aggression, so it is formed by adding a basic prefix onto the noun. In doing so, it breaks none of the exceptions to the rule: "aggression" is not capitalized, hyphenating the term doesn't avoid confusion, a vowel isn't repeated, the compound only consists of 2 words, and it is perfectly readable without a hyphen.

  • 2
    So where exactly does air-borne fit in this summary? It seems structurally the same as mass-produced - but imho that will always remain hyphenated, whereas it seems to me airborne is already the standard orthography. Commented Feb 28, 2012 at 23:59
  • 4
    This is one of those many cases in the English Language where the form follows the usage: there is no consistency or fixed rule for any of the usages. Airborne is airborne, rather than air-borne, because "it just is". You will normally find that people would understand air-borne or airborne to be the same word. It would be unlikely that it would be remarked upon. If in doubt, the hyphenated version will likely be read as intended, even if technically incorrect.
    – Jon Story
    Commented Feb 27, 2013 at 15:39
  • 5
    There is a prosodic reason for marking the separation of mass and produced in the written form of mass-produced (a slight pause in the spoken form); also asspr looks rather odd. On the other hand, one probably has to think for a couple of seconds before deciding that airborne actually is a compound. Commented Apr 24, 2013 at 16:55
  • 4
    @user1129682: Coordinate is not a compound word. It comes from the Latin coordinare, which is itself made of several parts. Commented Jul 20, 2015 at 19:49
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    What about words wich are separated such as post office? How can we distinguish them? Commented Oct 22, 2018 at 15:56

I recommend the following two articles:

Hyphenated Compound Words

Hyphenated Compounds: When and Why?

Unfortunately, the news in those articles isn't good. The distinction between hyphenated and non-hyphenated compounds is largely driven by convention, and while there are some rules of thumb, you have to be prepared for numerous exceptions and arbitrary differences between countries.

  • 1
    Could we have some excerpts showing why they are recommended? Commented Mar 12, 2022 at 16:37

I am not only a published writer, but I am also a trained court reporter and freelance proofreader/editor. Professionally, at least within the career of court reporting, reasons for hyphenating or not hyphenating certain words can vary. What follows are two reasons off the top of my head why one might see certain words (and even the same word) hyphenated one place and not another:

  1. Deposition agencies can have varied, and seemingly random, protocol for how they would like certain things done — including terminal punctuation of words within brackets or parentheses, citation of legal resources or statutes and, of course, certain words they do not want to see hyphenated. It would be fair to assume that publishing companies and news reporting organizations have similar guidelines that editorial staff are told to follow as well. I believe that different industries and fields of interest have some words commonly hyphenated which may differ from the way it is done elsewhere.

    Note: the rules of punctuation in court reporting can be very different from those of standard business English, creative writing, etc. I fought myself tooth and nail (tooth-and-nail?) trying to un-learn and re-learn rules.

  2. Laziness of writers (depending on what it is that you are reading), who seem to have little care if the reader understands what they are trying to say or not. It follows that then, I believe, "readability" is an extremely subjective term; maybe too subjective for some, which might cause issue.

  • There is also another major issue: How is the speech heard by the court reporter? There are often transcription errors or inaccurate choices made by court reporters. And it is not always their fault.
    – Lambie
    Commented Mar 11, 2022 at 16:59
  • The law is built on the same fantasy as many other things in our culture, that written words are the base, and spoken words -- especially words spoken by the poor -- are ethereal and irrelevant. Total bullshit, of course; it's the other way around. Commented Mar 11, 2022 at 21:01

There is an historical element to hyphenation. Compound words we commonly spell unhyphenated now were once two words. Then, as they became more commonly used, they became compound, hyphenated words. Finally, when used enough, they became one word. Usage seems to determine when a hyphen is used. The guide websites cited above suggest "consult a dictionary", but my 1890 Webster's Unabridged and my 1820 copy of Encyclopedia Britannica show very different usages of the hyphen from my current OED or American Heritage. (Some words reverse this process, as the "EnglishPlus" citation suggests, when they fall out of favor: "solid-state" becomes (currently preferred) "solid state".O

  • I am always pleased when reading ‘an’ in front of an unstressed syllable starting with H + vowel.
    – Canned Man
    Commented Mar 6, 2021 at 18:37
  • @Canned Man. We will agree to differ. Commented May 28 at 11:03

I found the following pages very helpful:

  • Compound Words which presents these rules:

    the closed form, in which the words are melded together, such as firefly, secondhand, softball, childlike, crosstown, redhead, keyboard, makeup, notebook;

    the hyphenated form, such as daughter-in-law, master-at-arms, over-the-counter, six-pack, six-year-old, mass-produced;

    and the open form, such as post office, real estate, middle class, full moon, half sister, attorney general.

  • Rules for Hyphens Between Words & Hyphens with Prefixes which lists a lot of rules for hyphenating, but whose main thrust is:

    Hyphens' main purpose is to glue words together. They notify the reader that two or more elements in a sentence are linked. Although there are rules and customs governing hyphens, there are also situations when writers must decide whether to add them for clarity.


There are certainly differences between US and Australian English, where we (Australia) have a tendency to hyphenate more than the US does. This is particularly the case where the un-hyphenated version is difficult on the eye: reenter, reelect, deescalate, and many of similar form.

In my part of the world these would normally all be hyphenated, except perhaps in the Murdoch newspapers, but even that is probably debateable.

I would think we also hyphenate almost all non- words (non-aggression, non-negotiable, etc). I also think hyphenation increases as the second word length increases.


Both your examples that do not have hyphens are words with negative prefixes. Words that include a negative (or positive) prefix will usually be written without a hyphen.

Examples: antimatter, indecisive, unwilling, probiotic, and nonaggression.

If the word includes an adjective that is neither directly negative or positive but is instead otherwise descriptive, then you should include a hyphen.

Examples: strong-armed, evil-minded, ill-adviced, and well-intended.

"well" is a borderline case, but it is not 100% positive. It's between neutral and positive, not one of those words you would use as a prefix in the same sense that you use pro, un, in or anti.

I hope this makes sense.

There are further prefixes that are neither positive or negative but still should not include a hyphen. I don't think it would be productive for me to quote the full list but words like extraordinary, infrastructure and transatlantic certainly seem to prove my theory a bit flawed. The point remains, however, that there are certain prefixes that are usually used without hyphen.

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