I would like to use a noun made of multiple words (like particle board, Mount Everest, or windscreen wiper) in a compound adjective with a hyphen. But I don't know how to hyphenate such a composition. I'm not sure how common this situation is, so here's an example:

Machine learning is a single noun made of two words, and I want to use it in a compound adjective with a hyphen.

Are either of the following examples correct?

  • I would like to pursue a machine learning-related certification.
  • I would like to pursue a machine-learning-related certification.

If not, then what is the correct way to hyphenate compound adjectives like this?

  • 2
    @EdwinAshworth That is not a duplicate of mine. "How to connect a word and a phrase with a hyphen?" is much less specific. That asker happens to use an example very similar to mine, but that does not make it the same question.
    – kdbanman
    Apr 10, 2017 at 22:52
  • It's essentially the same question, and answered there. Apr 11, 2017 at 10:23

3 Answers 3


Bryan Garner, Garner's Modern American Usage (2003) has a useful discussion of this problem in his lengthy coverage of phrasal adjectives:

E. The Compound Conundrum. When the first or last element in a phrasal adjective is part of a compound noun, it too needs to be hyphenated: post-cold-war norms, not post-cold war norms. Otherwise, as in that example, cold appears more closely related to post than to war.

In your example, machine learning is the compound noun and related is the additional element in the adjective phrase, so Garner would endorse punctuating it as machine-learning-related.

The Chicago Manual of Style, fifteenth edition (2003) takes essentially the same position as Garner:

5.92 Phrasal adjectives. A phrasal adjective (also called a compound modifier) is a phrase that functions as a unit to modify a noun. A phrasal adjective follows these basic rules: ... (2) If a compound noun is an element of a phrasal adjective, the entire compound noun must be hyphenated to clarify the relationship among the words {video-game-magazine dispute} {college-football-halftime controversy}.

Words Into Type, third edition (1974) emphasizes the practical goal to be achieved by hyphenating (or not hyphenating):

Phrases used as attributive adjectives usually require hyphenation to make clear their relation to the noun they modify.

[Examples:] the how-to-study area; a life-and-death struggle

If such a phrase modifier is hyphenated at all, it should be hyphenated throughout; but no hyphen should be used between the modifier and the noun.

Wrong: low milk-and-cream yielding dam

Right: low milk-and-cream-yielding dam

Wrong: pay-as-you-go-plan

Right: pay-as-you-go plan

If there is scarcely any possibility of misreading, hyphens need not be used.

[Examples:] a story and a half house; a thirty percent increase; yellow pine timber belt

All of these (U.S.) style guides agree that when ambiguity as to what is modifying what might ensue from an unpunctuated adjective phrase, it is better to hyphenate the elements of the phrase than to leave the words open. But the goal is greater clarity—and if the hyphens don't clarify anything, they have no business being there.

Thus far, my answer has focused on the "machine-learning-related certification" example in your question. Compound modifiers that incorporate proper nouns of two words or more (such as "Mount Everest–based climbing expedition") follow a different rule in these style guides: leaving the proper name open, and connecting the compound noun to the adjective with an en-dash instead of a hyphen. I won't go back into the reference works to quote the specific guidelines from each book, but they recommend the approach I have just outlined in this paragraph.

  • EDIT: I cannot really answer this question myself and find the answer of Sven Yargs interesting as well argumented. I wonder however how the rule he mentions would apply in two specific cases. ------------------ What about the following two cases? 1) A Monte Carlo-based optimization algorithm was used for this. 2) The Doppler RADAR-based detection system improves the robustness of overall airspace surveillance. These are typical sentences that you may find in scientific papers. My interpretation (as non-native speaker) is that it would be incorrect to write "Monte-Carlo-based" since "Monte Car
    – Nico
    Apr 10, 2017 at 11:39
  • ...lo" is a city name which is written with no hyphen (in English), but in the case of the Doppler RADAR only "Doppler" is a name and RADAR is an accronym (and pretty much accepted as a noun also). Does that make a difference? I find it quite odd to put an hyphen only between the last word (i.e. Carlo or RADAR/radar) and "based" in these examples. I could imagine a fully hyphenated spelling as for phrasal adjectives, but for names like Monte Carlo this does not seem right either. [second part of Nico's comment. --MetaEd]
    – MetaEd
    Apr 10, 2017 at 16:12
  • @Nico: U.S. style (at the book publishing level) favors using an en-dash instead of one or more hyphens with terms of the type "Monte Carlo–based." That is in fact the focus of the final paragraph of my answer, where the example given is "Mount Everest–based." As for your other example, if "Doppler RADAR" were a recognized proper or proprietary name, it too would (under Chicago and Words into Type guidelines) receive the en-dash treatment: "Doppler RADAR–based." But if radar is a generic descriptive word, we reach into a murky area where the style guides seem to leave the choice ...
    – Sven Yargs
    Apr 10, 2017 at 17:43
  • 1
    ... between hyphens ("Doppler-radar-based") and en-dash (Doppler radar–based") to the writer. Ultimately the style advice that these reference works offer hinges on how unitary the writer considers the base term to be: if "Doppler" is merely a descriptive term, you might leave the phrase open and use a hyphen for "radar-based" just as you would if you were talking about, say, "an old radar-based system": "Doppler radar-based." If the connection between "Doppler" and "radar" is close but not unitary, you might use two hyphens: "Doppler-radar-based." And if truly unitary, the en-dash approach.
    – Sven Yargs
    Apr 10, 2017 at 17:55
  • If I might throw in my tuppence worth of opinion: the second suggestion alone proves correct. Specifically: "I would like to pursue a machine-learning-related certification". Trickier proves compounding compound-adjectives, as in: "I would like to pursue a machine-learning-related, vocation-oriented, scholastic-refund-eligible certification." Apr 10, 2017 at 20:57

Alternatively, you could write "I would like to pursue certification related to machine learning."


The former is correct. Compound nouns within compound adjectives are not themselves hyphenated; only the other word boundaries are.

  • 3
    This smells right to me, thank you. I had trouble searching for this information though - where can I find a source for it?
    – kdbanman
    May 24, 2016 at 23:28

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