English spelling is difficult in itself, but to make matters worse there are two standard spelling systems, generally known as British and American spelling. When you choose the version of English that you use in Word, the program will automatically underline the words that are wrongly spelled. But it is still important to understand why those words are not right. Let us take a look at some of the main differences between British and American spelling.
Colour and color
In British English, some words end in “our”: labour, humour, flavour, colour, rigour, neighbour, candour. In American English, these words are written: labor, humor, flavor, color, rigor, neighbor, candor.
Theatre and theater
In British English, many words end in “re”: theatre, centre, litre, fibre, metre. In American English, these would be written: theater, center, liter, fiber, meter.
Defence and defense
In British English, some words end in “ence”, such as licence, offence, defence, pretence. In American English, these are written: license, offense, defense, pretense.
Analyse and analyze
British English users always write: analyse, catalyse, breathalyse, dialyse, paralyse. American users write: analyze, catalyze, breathalyze, dialyze, paralyze.
Travelled and traveled
Most of the time, when the final syllable of the root word is not stressed, the final consonant is not doubled when a suffix is added. However, in British English, the final consonant is always doubled if it is an “l”. So we write: travel, travelling, travelled, traveller, signal, signalling, signalled, signaller. American English is more logical, because the words ending in “l” follow the same rule as words ending in other letters: the last letter does not need to be doubled because the last syllable of the root word is not stressed. In American English it is correct to write: travel, traveling, traveled, traveler, signal, signaling, signaled, signaler.
Anaemia or anemia
British English preserves the “ae” and “oe” spellings used in classical Latin for scientific terminology: anaemia, haemoglobin, oedema, oestrogen. In American English these spellings are usually spelled with an “e”: anemia, hemoglobin, edema, estrogen.
Analogue or analog
The British English spellings analogue, catalogue, dialogue and monologue are sometimes maintained in American English, but sometimes the final “ue” (which is silent) is omitted. In American English it is quite acceptable to write: analog, catalog, dialog, monolog. Strangely enough, analog and catalog seem to be standard in American spelling, whereas dialogue and monologue are still found more often than their shorter equivalents.
The ise / ize difference is strictly speaking not a difference between British and American spelling: see ise and ize.