One person declines. Two or more people decline. I think "with regret" is presuming a bit. If you want to be very correct, don't send response cards at all. They were considered rude when I was married. The proper way for a guest to respond is for them to write a note. I would use the plural form on your cards.
I've always found the "happily accepts" or "regretfully declines" nonsense presumptuous as well. Some designer at some point must have started it and it stuck. I suppose I can think up something much more original. But if I run out of steam, I'll use the plural, declines.
Thanks for pointing that out. But we've decided to skip the word altogether in favor of:
(check box) We'll see you on the beach
(check box) Regretfully remaining stateside
I'm accepting full responsibility for the presumption of the word "regretfully." For some reason it pleased my Mom and it's not a hill I'm looking to die on.
I felt after some consideration though that accepts/decline(s) was a little too stuffy in an invitation that refers to our reception to follow as: dinner, tequila & shenanigans :-)
Re: Is it decline or declines?
If you want to be very correct, don't send response cards at all. They were considered rude when I was married. The proper way for a guest to respond is for them to write a note.
I would use the plural form on your cards.