When I write, I frequently use words with apostrophes. Examples are; doesn’t, hasn’t, shouldn’t, wouldn’t. All of these get the red underline treatment as if they were misspelled. Is there a simple way to let Scrivener know they are al intended, rather than having to add them one by one to the Project auto complete list? 
Spell-checking is handled by OS X, not Scrivener - try going to Edit > Spelling and Grammar > Show Spelling and Grammar and see what language is set. If it’s “Automatic by Language”, try changing it to English.
All the best,
Keith
Keith many thanks - I much appreciate your advice. Cheers, Richard