Ise and ize endings

One of the first and basic questions I ask when taking on a new project is whether my client has used -ise or -ize word endings. One of the most important aspects of proofreading is ensuring consistency – I’m not just looking for “right” or “wrong” spellings.

SpellingThe use of -ise and -ize word endings is generally a matter of choice, except for some words where a certain spelling is compulsory. For example, advertise, devise, improvise, prise and surprise must all be spelled with -ise. (If you spelled prise with -ize you would be using a different word!)

The compulsory -ise spelling is usually for words that are derived from French. A legitimate choice arises for some words because -ize corresponds to the Greek infinitive ending which made its way into English via Latin and French sources. In French, the spelling was adapted to -ise and many English writers followed the French lead. It is important then to note that, while -ize is the preferred ending in American English, the use of -ize is not an Americanism nor is it restricted only to American writers. The -ize ending has been a feature of English since the 16th century.

English users therefore have the choice of whether to use -ise or -ize endings. If you are working to a particular style, you will often find that a preferred form has already been designated. For example, Oxford University Press traditionally uses -ize spellings.

The most important points here are as follows:

  • Not all words have the legitimate choice between -ise and -ize endings. If you aren’t sure, a good dictionary will help.
  • For all other words, it doesn’t really matter which form you choose. However, it does matter that you are consistent about using your preferred form (and that you tell your editorial professional which form you chose!).


  • Fowler’s Dictionary of Modern English Usage, ed. Jeremy Butterfield
  • New Hart’s Rules, 2nd Edition

8 thoughts on “Ise and ize endings

  1. Thanks for enlightening me.
    I had it in my mind ize was an American feature.
    This might explain why Word Spellcheck is insisting of ‘ize’ endings (and maybe one contributing factor to the absence of the ‘language’ option in Spellcheck).
    There’s always something new to learn (and something extra to watch out for when re-reading your writing project for errors etc)


    • Yes, that is common – but it is worth keeping in mind if you are writing for an American audience that they will expect ize endings. Consistency with ise and ize endings is one of the basics I think any writer will find it worthwhile to think about.
      (I find the lack of a language option in spellcheck frustrating sometimes but then I try to see it as a way to make sure I don’t start on a slippery slope to complacency.)

      Liked by 1 person

      • Thanks for that advice. I am working on a fantasy novel which is aimed for the broad English speaking population, so the ize would be the wise move (Ah well Ctrl & F followed by ‘Replace ‘ option, let’s see how well you handle this one!)

        Liked by 1 person

      • You are very welcome, and I agree – ize is probably the best choice for a broad audience. But I must advise keeping your wits about you when using find and replace! It is responsible for errors even in traditional publishing.

        Liked by 1 person

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