An SOP is a Standard Operating Procedure. I think that in the case of deciding who gets/doesn't get a wedding invitation, a couple needs to write down a set of guiding principles, otherwise cutting down the list seems arbitrary and unfair.
I've been thinking about this because one of my best friends from college (and actually camp, before that) is getting married, and she and her fiancee are having some difficulty over the guest list. Essentially: he wants to invite everyone that he's ever met, and she does not. When you have 70 guests to split between the two of you it gets a bit touchy. In order to mediate this, I have created a set of SOPs for guest invitations:
I. Required Guests (in descending order of importance)
i. immediate, plus one level (a "removed" or "second") if you see them on a regular basis
ii. anyone that will give you an awesome present/remember you in the will
i. Best Friends
a. from childhood/high school, as long as you keep in touch regularly and have seen them within the last year (exception for those abroad)
b. College Friends-- keep these to a minimum, they probably don't have enough money to pay for a nice gift. Also, unclear how close to them you will be in five years.
C. People Who Will Be Really Angry If You Don't Invite them
i. in this case weigh the social discomfort of the lack of invitation against how much you actually want the person to be at your wedding
II. People About Whom You Are On The Fence*
A. More Distant Family
i. those who give great presents/are fun at a party are in
ii. also include those who will be REALLY insulted if they are not invited
iii. do not include those with whom you/your parents/relatives have had a 'falling out'
B. Not As Close Friends
i. You must have seen this person (in person) at least ONCE in the previous calendar year, preferably pre-engagement, you must speak to them no less than once every six months, and you have to actually enjoy their company
C. People Who Will Be Insulted, But You Care Less
i. same criteria as above
III. People Not To Invite
i. Black sheep of the family, unless it will be really fun
ii. very distant relatives, except as a courtesy
i. former best friends that you haven't spoken to in forever
ii. anyone who doesn't return your calls/letters in at least a 2:1 (yours: theirs) ratio.
C. Those Who Will Be Insulted
i. people who you either don't care about, or who won't find out
i. with very few exceptions, these people are not your "real" friends.
*Appendix A: What to do about those on the fence
Make a list in descending order of those who you wish to invite but cannot due to space concerns. They are your second run. Alternate a person you wish to invite with one whom your fiancee wishes to invite, and when someone RSVPs in the negative (from one of your original guests, not those assigned to either your, or your fiance's parents) you may move someone up from the "bench" to the "field" and send them an invitation.
Disclaimer: this document is intended for humorous purposes only, and is not to be applied by real couples with actual weddings.