The most common spelling mistakes are those in which the wrong version of English is used. A surprising number of people don’t realise there are often major differences between UK and USA spelling and grammar (other countries have differences too, but I’ll focus on UK and USA, as they’re the most widely used). The differences are because, while the English language keeps evolving, American English still largely follows the early 1800 rules of American lexicographer Noah Webster, as detailed in his An American Dictionary of the English Language (1828).
Before Webster’s dictionary, it was acceptable worldwide to spell many words in two ways, as those words were introduced into the English language from Latin and French, and the spellings differed accordingly. Webster, however, wanted American spelling to be distinct from British spelling.
Most countries today follow UK spelling and grammar rules, with Canada and Australia as examples of countries that tend to follow both UK and USA rules.
Whichever spelling you choose, it’s important to be consistent. Writers in countries that accept both spellings (and a mixture of UK and USA) are still under advisement to use just one or the other, as most books are distributed internationally, and most international readers are not aware that, in your country, this is correct – they will assume you just don’t know how to spell or that your book has been badly edited, and that’s obviously not the image one wants to put out there.
Some rules of thumb:
Words ending in -ize are probably USA spelling, and words ending in -ise are probably UK spelling. For example, ‘realize’ is the USA spelling of the UK’s ‘realise’.
Words ending in -er are often USA spelling, and words ending in -re are probably UK spelling. For example, ‘theater’ is the USA spelling of the UK’s ‘theatre’.
Words ending in -or that drop the ‘u’ are usually USA spelling, while UK spelling retains the ‘o’. For example, ‘color’ is the USA spelling of the UK’s ‘colour’.
Words ending in -yze are usually USA spelling, while words ending in -yse are usually UK spelling. For example, ‘analyze’ is the USA spelling of the UK’s ‘analyse’.
There are, however, some words that should always be spelt one way or another, regardless of which English version you’re using, despite the fact that they technically fall into one of the above categories.
Words that should always end in -ise:
Advertise; advise; apprise; arise; chastise; circumcise; comprise; compromise; demise; despise; disguise; devise; enterprise; excise; exercise; franchise; guise; improvise; incise; merchandise; promise; revise; rise; supervise; surmise; surprise; televise; wise
Words that should always end in -ize:
Words that should always end in -re:
Acre; massacre; mediocre; ogre
Words that should always end in -er:
Chapter; December; disaster; enter; filter; letter; member; meter (measuring device); minister; monster; number; November; October; oyster; parameter; perimeter; powder; proper; September; shoulder; sober; tender
I hope you find this information helpful.