Ok - we can’t go to the wedding. The enclosed card says “The favour of a response is requested by January 15” Then it has a space for Name and Number of guests. How do we inform them on this card that we are not going to attend? Or do we have to write a note? Help.
If there is no space on the card for regrets, then they messed up. You might simply write on the bottom of the card “We’re so sorry we will not be able to attend. Best wishes, CC.” and send it back in the self-addressed, stamped envelope that should be provided.
If you are so inclined, you could send a card as well, probably closer to the date of the wedding, offering your good wishes and saying again you are sorry you won’t be attending, but this isn’t required. The response card is exactly that, the means by which you respond to the invitation.
Miss Manners would prefer that, even if you are going, you throw away the card and write a personal note advising of your delight to attend.
If you have no personal stationery lying around and want to use their card, just write a one-line response, “Sorry, we will be unable to attend; hope it will be a most wondrous day.” and send it back.
(Don’t forget to put an extra penny stamp on it since they probably sent it out with a 33 cent “Love” stamp that is now inadequate to get it back to them.)
Hmmm, my choice would be to enter my name in the space, and “-1” as number of guests. That way the count for the caterers would be correct, but it wouldn’t be obvious you weren’t going.
But perhaps that’s not proper etiquette. 
You could always sell it on ebay - I bet SOMEBODY would bid for the free food at the reception
Arjuna34
As was all ready said, a short note is fine. Most of the no responses for our wedding had a little line showing the invitee regretted not being able to come, yadda yadda.
[rant]I hate response cards. I’m not an etiquette-idiot, I know how to properly respond to a formal invitation! The response cards make me feel as if the sender doesn’t trust me to behave appropriately. I used to tear the response cards up and send back a proper written response on my own paper. However, response cards are now so ubequitous that a proper response seems rude – as if I was instructing the sender on proper behavior… So, I have the choice of being rude (sending a proper written response) or improper (I don’t care, a response card is not correct!). Also, most brides who send out the response cards keep a little file with the responses in it and my letter wouldn’t fit in the box… So, I send back the response card and just feel wrong about it![/rant]
As has been stated, the “proper” way to regret on a response card without a regret option is to cross out the printed line and write in a line of regret above or below it. Of course, if people insist on sending the damn things, they ought to at least have the decency to buy the kind that have a ‘regret’ box to check!
As one recently involved in sending out (and receiving) a lot of response cards to wedding and reception, I am grieved to say that while you, Jess, may not be an “etiquette-idiot,” you are sadly in the minority. The variations we recieved in response to our invitations made me despair for the future of mankind.
- Rick
Response cards may be “improper,” but these days they are expected. I didn’t want to include them, but my mother made me, and I’m glad she did.
The ones we sent out just said “please respond by xx/xx.” They were blank otherwise, so people could write what they wanted. The responses were delightful. It was a real treat to read them. The people who were so inclined wrote their “proper” response right on the card. It was a good compromise solution.
You’re not alone, Jess. I’m not an etiquette idiot either, but sometimes I would like to be able to show that my mother’s lessons in manners weren’t totally wasted. When I receive an invitation with a response card, it’s usually of the sort where I can respond either way: it has a blank or a checkbox or something of that nature. I use it; it’s not my first choice, but it’s there.
However, if we receive a response card without a clear indication of how to accept or decline like CC mentioned in the OP, then I get to recall my mother’s lessons–I write a note, worded something like the following:
“Mr. and Mrs. Spoons regret that they will be unable to attend the wedding of Jane Doe and John Smith on Saturday the 6th of January, 2001, at Anyfaith Church, and afterwards at Anytown Country Club.”
That’s the important line, CC, and you don’t have to give a reason. After that sentence, you might add a wish for future happiness or something, but that’s not absolutely essential.
It’s not a difficult task to write a note declining an invitation–use a good notepaper and keep it short. Besides, especially with regrets, it’s sometimes easier than trying to figure out what the card wants you to do.
Greenbean
We also used blank cards for our responses (we may have put the date on there, can’t remember). Since we were printing the invitations ourselves, we weren’t constrained to “standard” formats. This way everyone has to write something. We kept the cards and enjoyed reading the responses. Some were amazing - people profusely apologizing that they couldn’t make it. It was really neat. If anyone were to ask my opinion about them, that would be my recommendation.
Most response cards have a nice clean BLANK side, if there isn’t room on the response side to write your note… That way it still fits in their little box. I’ve turned a few of the fold ones inside-out to get a clean side to write the note on. Just put it in the return envelope with the note visible, so they don’t think you forgot to write a reply entirely.
As epeepunk noted, we got some great replies by sending blanks (I do think we put an RSVP date on them, discretely in the corner, as well as stamps). Got some beautiful lettered ones, too, IIRC. I don’t recall any frustration at people ‘getting it wrong’ - we just expected them to get it right (or close enough), and they did - around 350 people invited, too, so there was plenty of sample. Now, people inviting themselves to the wedding (or better, suggesting cattily that perhaps we overlooked inviting a whole family of six who would just love to come), frustration doesn’t come close…
[aside to epeepunk] hi, babe! [end aside]
I’ve never recieved a blank response card – actually, this strikes me as a good compromise. And, believe it or not, hedra, it never occured to me to turn the damn thing over and write the response on the back. I’m not an etiquette-idiot, anyway! 
In thinking about it, I believe I overstated my previous objection. I think that the etiquette on this issue is in a state of flux. It is still correct to respond to a formal invitation with a handwritten response following the format of the invitation. However, that doesn’t really make response cards incorrect – more like option #2 and rising. As Greenbean said, they are more and more expected. Etiquette being a more fluid thing than generally believed, response cards may become option #1, although I don’t believe that a handwritten response will ever become improper. In fact, among my husband’s relatives it would probably be considered rude not to include response cards. Before I was married, I never sent commercial sympathy cards – I always sent a personal, handwritten letter on my good paper. Soon after I was married, my mother-in-law told me that not sending a card looked “cheap.” She was wrong, of course, and my handwritten letters are perfectly correct – more so than a printed card – but it didn’t seem important enough to argue about. So, now I keep a few sympathy cards on hand for his side of the family (and write my note inside). His family would surely consider the lack of a response card in a wedding invitation rude. Furthermore, they would consider my replacing the response card with a correct handwritten response to be both uppity and bizarre.
However, there are limits. I wouldn’t put a registration card in the invitation (which they all do) – even when my mom-in-law tried to insist. Etiquette does have some gray areas, and I’m willing to admit that response cards and sympathy cards are in that zone, and towards the whiter end, too. However, registration cards in an invitation are just tacky, tacky, TACKY!
Etiquette-Jess, putting her foot down!