Over the past several years, we have had several ‘extra’ dances here in Tallahassee that are advertised to the contra dance listserv and elsewhere as old-time or square dances, or old time square dances, with live music. We have had anywhere from 8 to 30 dancers come. One of the things we heard from dancers was that they did not like being left out — wanting to dance but not enough dancers for a full square. We decided on a policy of leaving no-one sitting who wants to dance. That means that we don’t decide what dance to call (at least not for sure) until we see how many couples stand up to dance; and it means that I have dances ready to go for 4, 5, 6 or 7 couples. With 6 or 7 it can be a longways set, a contra, a circle mixer, or a big circle square-dance. With 8 or 12 it’s a 4-couple square. Folks seem to appreciate the concern for their enjoyment, and there are plenty of good dances to choose from for any number of couples. (Although I could wish for more good five-couple dances, the vast repertory of circle mixers comes in handy.) I have also used a couple of 6- or 9-couple dances I learned from Phil Jamieson.
Others have recently dealt with the situation where you have only three or even two couples.