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Why we check in at the CHECK-IN and check out at the CHECKOUT – OR: Is the spelling of English compounds really chaotic?

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This guest post is by Christina Sanchez-Stockhammer, who is Senior Lecturer in Modern English Linguistics at LMU Munich. She has published on a large variety of topics, such as the word-family integration of the English lexicon, the language of comics, the corpus-based English and German translation equivalents of the times of day, and the question whether one can predict linguistic change. For further information, see www.christina-sanchez.de.


Many years ago, I looked for the compound sand castle (spelled with a space between its two parts) in an electronic English dictionary, but my search yielded no results. Since I was sure that the word was common enough to be in that dictionary, I tried the alternative spelling sand-castle. The hyphenation brought up a list of words introduced by Did you mean… , but only the single-word spelling sandcastle took me to the dictionary entry I was looking for. This made me realize that the question how the parts of compounds are linked is both relevant and interesting.

Whenever we spell a compound, we are forced to pick just one of the alternatives. The problem is that many English language users believe the spelling of English compounds to be chaotic. This is possibly because some compounds like girlfriend/girl friend or flower pot/flower-pot are spelled differently not only in different texts but even in different dictionaries. However, we can also observe that other compounds are very stable: they are usually spelled in one particular way only, or never occur with one of the possible spellings. This can be shown very nicely with the made-up sentence:

It was not very farsighted of our local agonyaunt to celebrate her birth-day with so many cock tails.

– which looks quite strange compared to

It was not very far-sighted of our local agony aunt to celebrate her birthday with so many cocktails.

with the more usual spellings.

All of this made me wonder whether the spelling of English compounds is really completely random or whether we can recognize some underlying system if we look hard enough: is there anything that all the compounds that are usually only spelled with a space have in common, and which sets them apart from all the compounds that are usually only spelled with a hyphen or only as a single word? And if yes, can we use this knowledge to work out the most likely spelling of compounds many people feel uncertain about?

To answer these questions, I compared the spelling of about 10,000 compounds across six dictionaries by different publishers (Macmillan Dictionary being one of them) and coded how often they occur in the language, how long they have been around, which of the parts receive more stress when spoken and many other things for 600 of them. In the end, it turned out that the spelling of English compounds is connected to an overwhelmingly large quantity of different things. That is what makes spelling English compounds so confusing. But on a general level, it all boils down to a few very simple principles, which work for three out of four compounds with two parts:

  1. Use a hyphen in compound verbs (blow-dry), adjectives (world-famous) and adverbs (well-nigh).
  2. Use a space in noun compounds with three or more syllables (bathing suit).
  3. Use a hyphen in noun compounds with two syllables whose second part has two letters (make-up).
  4. Spell noun compounds with two syllables whose second part has more than two letters as a single word (coastline).

This strategy is so simple because word class and length are connected to many of the other meaningful aspects that play a role in English compound spelling. The rule of thumb can also help you understand why check-in in the title of this blog post is spelled with a hyphen and checkout as a single word: what may have initially seemed arbitrary and random now appears as a systematic variation between two-syllable nouns whose second part has two letters vs. two-syllable nouns whose second part has more than two letters.

If you would now like to learn more about my research on the spelling of English compounds, feel free to take a look at my website How to spell English compounds in two simple steps. The website also contains a video tutorial and a webtool that gives you the most likely spelling for the compounds you type in. If you are interested in even more details, you can find the full story in my book English Compounds and their Spelling (Cambridge University Press, 2018).

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Christina Sanchez-Stockhammer

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