Spelling: -ise or -ize?

American and British usage differs, and is not always consistent, so this is a recurring headache for writers and editors. In general, American English uses –ize, whereas British English uses –ise. Consistency, of course, is everything. Consult the House style, where there is one.

Here are some basic guidelines.

1. In British English, many words ending in –ize can also be spelt –ise. Examples are mechanize/ mechanise; realize/ realise; organize/ organise.

2. However, in British English some words must be spelt –ise. Examples are: advertise, comprise, compromise, enterprise, exercise, supervise, televise. (This is why the general rule about using –ise for British English applies.)

3. A similar problem arises with –yse and –yze. Examples of words that should be spelt –yse in British English are: analyse, catalyse, paralyse. (American English would use –yze.)
When in doubt, consult your dictionary, which should give variant spellings. [For more a complete list, consult Butcher’s Copy Editing (6.14).]