Many British English speakers disapprove of spellings such as ‘criticize’ or ‘modernize’, as if the letter ‘z’ were some devilish American plot designed to ruin ‘traditional’ English spelling forever.
Yet if these same diehards were to pick up a novel by, say, Charles Dickens, Thomas Hardy or George Eliot, they might be surprised at the sheer number of words spelt in this way: ‘apologize’, ‘organize’, ‘recognize’, ‘sympathize’, ‘utilize’; the list goes on.
In fact, in the literature of the 19th century this spelling is far more common than the alternative ‘-ise’ which many English children are still taught at school today.
The spelling with ‘z’ is preferred by the vast majority of British authors and editors from the 18th century to the present. It derives originally from the ‘-ize’ ending of Greek words such as ‘ostracize’ and ‘baptize’. And to this day the Oxford English Dictionary gives ‘-ize’ as the preferred spelling, listing ‘-ise’ only as a variant.
Of course there are always detractors who insist on using the French-derived ‘-ise’ for all verbs, irrespective of the words’ origins. Among their number are Emily and Charlotte Bronte (but not sister Anne), and the Times newspaper (which changed from ‘-ize’ to ‘-ise’ as recently as 1992).
As you might expect, there are exceptions to everything that I have written above. These include verbs whose Latin stem ends with ‘-vise’ (‘advise’, ‘devise’, ‘supervise’), ‘-prise’ (‘surprise’, ‘comprise’, ‘reprise’), ‘-cise’ (‘exercise’, ‘circumcise’) or ‘mise’ (‘promise’, ‘compromise’, ‘surmise’). All should be spelt with ‘s’, as should ‘analyse’ and ‘catalyse’, both of which share the Greek stem ‘-lys-‘, from the verb ‘luo’, to loosen or untie.
Some exceptions to the rule:
advertise
advise
analyse
catalyse
circumcise
comprise
compromise
devise
exercise
promise
reprise
revise
supervise
surmise
surprise