Using an ‘s’ over a ‘z’ is one of the most obvious differences between Australian English and American English. It’s an area of huge debate—when are grammar rules of opposing English-speaking countries ever not?—but also of huge confusion. Everyday grammarians are aware that some words must include a ‘z’, no matter the country it is used in. But which words are they? And why are they so?
‘Z’ is a letter long misrepresented. Though American spelling uses the –ize ending almost exclusively, it is not of American origin. The suffix originates from Greek –izein, via Latin –izare. –ise, on the other hand, comes from the French –iser. France started to spread its linguistic influence during the 19thcentury, around the same time American lexicographer and spelling reformer Noah Webster was singing the praises of ‘z’.
Words that demand –ize include: capsize, seize and prize (as opposed to ‘prise’). Scientific terms, such as oxidize and synthesize, are not necessarily correct, but are taken as the standard in international scientific publications.
Similarly, there are words that demand an –ise: advertise, advise, apprise, arise, chastise, circumcise, incise, excise, comprise, compromise, demise, despise, devise, disguise, exercise, franchise, improvise, merchandise, revise, supervise, surmise, surprise, televise … etcetera.
And then there’s the batch that straddle the continents: analyse, authorise, customise, organise, summarise … etcetera. These are the ones that somewhere mid-Pacific, transpose the s for a z.
According to the Macquarie Dictionary, Australian English prefers the –ise spelling at a ratio of about 3:1. Indeed, as one can see, using –ise as a default requires far fewer exceptions to be made. So not only is it likely to be more accurate, it’s also easier on the speller.
The Oxford English Dictionary shares its thoughts:
‘[T]he suffix …, whatever the element to which it is added, is in its origin the Gr[eek] –?????, L[atin] –iz?re; and, as the pronunciation is also with z, there is no reason why in English the special French spelling in –iser should be followed, in opposition to that which is at once etymological and phonetic.’
Basically; make your life easier. Go with –ise.