So, what do dancers need to know in order to progress through a duple contra dance?

(1) At the end of a swing, who finishes on which side. Thus we need some words and concept of these two roles, whether  men and women, larks and ravens, or P's and Q's.  (This seems  really important when neighbors swing, and less important in ECD.)  

(2) The identity of their current and future neighbors.  (Tells dancers which way they are progressing.)

(3) A consistent way to designate positions within a group of four.   For the moment consider  "first corners" to be the positions of woman 1 and man 2 at the start of the a duple improper dance.

Prudent use of all of these seems  important over the various contra formations:  improper, proper, becket (progressing left or right), indescent (2's crossed), and dances where the "1's" (those moving away from the music)  start below the "2's." 

For beginning and intermediate dancers, callers' use of (1) is often easier than (3).  

In dances with unusual end effects, caller's use of (3) can be difficult.     

   

In general using (1) is clearer, because (a) it is easier to find a person, and (b) one's position changes throughout the 32 seconds or so of a contra. 

I can think of quite a few dances which become much more difficult to convey to the dancers when (1) is avoided.   For example: 

(a) "Second corners chain on the left diagonal" will always seem obscure.

(b) Who rolls in front during a roll away, or moves in front during a Mad Robin

(c) dances with partial heys 

(d) Many proper dances