Most translators and editors work on the basis that the -ise suffix is British and -ize is American. So we have realise/realize, advertise/advertize, analyse/analyze, as well as the derived forms realisation/realization and so on.
As usual, the reality is more complex. Here are some things which upset the simple rule:
- There is no rule that British spelling must use -ise in words like “realise”. Pick up any book published by Penguin, for example, and you’ll find they standardise on -ize. The OED (Oxford English Dictionary) prefers and recommends -ize, with -ise as an optional alternative, but in practice a majority of Brits (and Australians) use -ise.
- Just as Brits tend to assume -ise is always correct, Americans tend to assume -ize is the only form for them. In fact, the following have -ise in all cases, in both Britain and America (check with www.merriam-webster.com if you don’t believe me):
seise (legal term)
- (from Judith Butcher, Copy Editing for Editors, Authors and Publishers: The Cambridge Handbook, Third Edition, 1992, p. 160)
- There are a few words where -ize is obligatory too, such as capsize, size, seize and prize (when it means “appraise”).
- Curiously, this means that if you use -ize for the cases which are optional in Britain and -ise for the obligatory ones in both countries, you end up with spelling which is acceptable on both sides of the Atlantic.
- We tend to assume that British spellings are older than American, and that it was Noah Webster who instigated changes such as colour/color, draught/draft. But in this case it’s the -ize forms which are traditional, (via Greek and Latin) and it was Britain which changed over to the more French-looking -ise forms in the last couple of centuries.