If you come to contra dance from a different tradition, or you're a DJ putting together sets for a techno contra, people will tell you to choose "square" tunes with "clear phrasing". What does this mean?

In contra dance you take one step for every beat of music, and it's all built around powers of two:

• 2 beats: roll away, pass through, pull by.
• 4 beats: balance (which is two 2s), petronella and rory-o-moore spins, turn as a couple.
• 8 beats: long lines, chain, right and left through (all of which are two 4s)
• 16 beats: balance and swing, full hey

The music is also generally built around powers of two:

• 64 beats: once through the tune
• 32 beats: the A part vs B part
• 16 beats: a section of the tune (A1, A2, B1, B2)

This looks like:

      tune
    /      \
   A        B
  / \      / \
A1   A2  B1   B2

Each section (A1, A2, B1, B2) then also divides into powers of two, with two clear 8-beat phrases, each of which generally has a clear 4-count and 2-count.

These power-of-two figures generally need to align with the powers of two in the music. So while you could have a dance that did:

• (4) balance
• (2) roll away
• (2) roll away
• (8) long lines

a dance that did:

• (4) balance
• (8) long lines
• (2) roll away
• (2) roll away

would be very strange. When you look at the structure of a the tune you can see why the that doesn't work:

          64
         /  \
        32   ...
      /   \
     16    ...
   /    \
  8      8
 / \    / \
4   4  4   4

The former is fine:

           16
          /  \
         8    long lines
        / \
 balance   4
          / \
      roll   roll

but the latter doesn't fit well:

              16
          /        \
        8            8
       / \          / \
balance  lines  lines   4
         go in  go out / \
                      /   \
                  roll     roll

Of course, a dance could be an even worse fit. Consider:

• (2) roll away
• (4) balance
• (8) long lines
• (2) roll away

Or:

• (1) stamp
• (2) roll away
• (4) balance
• (8) long lines
• (1) stamp

These fit the tree so poorly I'm not even going to try to sketch what they could look like.

Now, some figures don't exactly fit a tree. The main exception is the swing which always runs until the end of the current sixteen count:

• (2) pass through
• (14) swing

or:

• (4) balance
• (12) swing

or:

• (6) circle 3/4
• (10) swing

or:

• (8) larks allemande left 1.5
• (8) swing

These can look a little strange:

          16
         /  \
        8    more swing
       / \
balance  swing

but the key thing is that the swing has to finish the 16 count. So you can have:

• (8) half hey
• (8) swing

but you can't generally have:

• (8) swing
• (8) half hey

This means the dancers need to be able to hear the 4 count, 8 count, and 16 count to figure out when to start and end figures.

What about the 32 and 64 counts? They keep the dancers from getting lost. Consider the dance, The Baby Rose:

• A1
  • (16) Neighbor Balance and Swing
• A2
  • (8) Circle Left
  • (8) Dosido Partner
• B1
  • (16) Partner Balance and Swing
• B2
  • (8) Ravens Chain
  • (8) Star Left

Notice how both the A1 and B1 are a balance and swing, but then people need to do different things in the A2 (circle) vs B2 (chain)? When you play a tune that has two clear sections of 32 beats (and "A part" and a "B part") and that clearly signals the 64-count ("top of the tune coming up!") the dancers are much less likely to accidentally circle when they should be chaining.

A "square" tune is one that breaks down into our nice even tree:

          64
         /  \
       32    ...
      /  \
     16   ...
   /    \
  8      8
 / \    / \
4   4  4   4

It supports the dancing, and makes it easy to hear where the figures go. When you're playing, or picking tunes, you want to make sure that each of these different levels of the tree will be apparent to the dancers.

Now, different dances need different things. For example, here's the B2 (last 16 counts) of Chuck the Budgie:

• (4) Balance short wavy lines
• (4) Neighbor allemande left 3/4
• (4) Balance long wavy lines
• (4) Next neighbor allemande right 3/4

This dance would go great with a tune that really gave a clear four count ("chunky") while a B2 of:

• (16) right shoulder round, and swing

is going to go a lot better with a tune that doesn't emphasize fours or even eights, and just lets the dance flow.

While you're unlikely to find a tune that has exactly the right rhythmic structure to support a particular dance, you also have a lot of freedom in how you play the tune. For parts that are flowy with long figures and mushy transitions (hey into right shoulder round) then don't accent the 4 or 8 and let the structure of the tune indicate the 16/32/64. Similarly, if the transitions are precise (balances, lines) then make a clearer break.

If you're playing for a dance and choosing standard 32-bar jigs and reels most of this will come very naturally. On the other hand, if you want to take pop songs and DJ them, you're going to run into the problem that they don't tend to have this "square" structure. They often have an 8-count, but they probably don't have all the levels of the tree up to the 64-count. You can pick songs that do, modify ones that don't, or just go ahead with things that don't have clear phrasing (that's what people usually seem to do). One thing I'd love to see someone play with is adding a tiny bit of extra embelishment on top of songs to signal the 16-count, 32-count, and 64-count.