The Remedy of the Week: -ise or -ize?

Each week proofreader Hannah Jones discusses and offers a remedy to common problems we encounter when writing. Today she explores when to use -ise and -ize endings.

Why does it matter?

One of the most common errors I come across when proofreading is inconsistency of verbs ending in -ise or -ize. If a word is spelled with the -ise ending on one line and the -ize ending a few lines later, this can look very clumsy. Inconsistency in spelling can distract the reader from the text; if they are doubting how something is written, they may begin to doubt what is written, too.

Which is correct?

In British English either ending, -ise or -ize, is acceptable. It is simply a matter of preference or referring to a house style. The Oxford Style Guide prefers -ize spellings while many other universities prefer -ise spellings. Neither ending is more 'correct' than the other; what is important is that, whichever form you choose, you use it consistently throughout a piece of writing. 

Words that always end -ise

It's important to remember, however, that some verbs always end -ise. This reflects the fact that these verbs are not formed by adding -ise or -ize to a noun (as in the case of verbs such as hospital+ise/hospital+ize); rather the -ise forms part of a larger word element such as -cise (meaning 'cutting') in excise and incise, or -vise (meaning 'seeing') in revise and supervise.

Some of the most common words which must always end in -ise, even if the -ize system is being used, include:

advertise, advise, arise, comprise, compromise, despise, devise, disguise, excise, exercise, improvise, incise, reprise, revise, supervise, surprise, televise.

-yse or -yze?

While either -ise or -ize is acceptable in British English, -yze is not. So, in British English, words such as analyse and catalyse cannot be spelled analyze and catalyze.

In American English, however, the -yze ending is preferred. 

The Remedy

  • In British English, use either -ise or -ize endings consistently
  • In American English, use -ize endings
  • Remember verbs such as advertise and comprise always end in -ise
  • Use -yse in British English and -yze in American English

Most importantly, remember that consistency is key. Writing free from inconsistencies allows the reader to focus on what you're writing about, not how it is written. If you're finding it hard to keep track of all your style choices, you may wish to consider hiring a proofreader to help you.


Ritter, R.M., 2005. New Hart's Rules: The handbook of style for writers and editors. Oxford University Press.

Hannah Jones is a professional freelance proofreader and owner of The Remedy of Errors.

Visit her website at The Remedy of Errors. She can also be found on Twitter @remedyoferrorsFacebook and LinkedIn.