In Chapter 29 there is an lengthy discussion of who to invite to the dance, with the comment that such would make up five couples.

From my experience with English Country Dancing, five couples is the minimum number. It is possible to have a dance with less, but it doesn't work out as well.

If you're dancing a "Duple-minor" where each pattern requires an "Active" and one "Passive" couple, five allows for four repeats for the Actives to get to the bottom of the set. To get to the Top again, gives 16 repeats. Five also allows for two Active couples (the original from position three onward and the new Top couple) dancing at the same time. This provides a much more interesting appearance. You could do the same with four couples, but each Active only gets three repeats, or nine for the entire set.

If you're dancing a "Triple Minor" each Active couple gets three repeats. This puts them into fourth place, from which they "Cast Off" to the bottom, and the fifth place Casts Up into Fourth Place, while the new Top Couple starts. With only four couples, the bottom pair casting up has to leap into the Triple-Minor as a new third couple. It can be done, the Regency Dance group I belong to has done it (including at tome demonstrations) but it is a tricky transition (one we had to practice repeatedly).

For all of the above, a sixth couple enlarges things considerably. With five couples, a dance might only last a few minutes (for our demos, the group found five ideal, otherwise the audience lost interest). With six, a Duple-Minor now gives five and twenty-five repeats for the entire dance. It works on the (x-1) squared formula - you easily see how long a ten couple set could go on.) Six also allows for three Minor-Sets in a Duple, and two in a Triple.