Complete stability is stillness. In any position off the floor, a still body is actually making constant, minute adjustments to remain balanced, but most of these adjustments are invisible from the outside.
Only when a body is destabilized, or imbalanced, does it start moving perceptibly. Destabilization leads to movement, which breaks rigidity in the body, and this leads to controlled falling, which is one fundamental approach to understanding dance. Music which alternately emphasizes the pulse and has syncopation (notes or emphases which fall between pulses or beats), destabilizes the pulse and propels the moving body. Here's an example:
Consider the 3-3-2 rhythmic pattern. It is common or at least present, in one form or another, in pretty much every musical tradition that I know of, especially in music that people dance to. In fact, it is /central/ to many types of dance music. Listen to some Calypso music from Trinidad and Tobago, or the music of Cesaria Evora or Lura from Cape Verde. You'll recognize the "long, long, short" pattern. Try clapping it. The Xs are claps and the -s are rests*:
||: X - - X - - X - | X - - X - - X - :||
... try counting out loud while clapping:
||: "1 2 3 1 2 3 1 2" | "1 2 3 1 2 3 1 2":||
Why is this rhythm so common in dance music? I think it's because it has a perfect balance of stability, destabilization, and propulsion. Let's take a tour through one cycle of this rhythm, with a little analysis:
STABILITY: The first note is fully stable and grounded. It is the "big" beat and has the least potential energy.
DESTABILIZATION: The second note is an upbeat, it's syncopated, unstable, and has the most potential energy, which is released and drops us from the furthest height on our way back to landing on the stable downbeat of the next cycle. The syncopated second note causes an undulation in the body, around the beat. I feel like it has an "up-ness" and movement "bounces off" this note.
PROPULSION: Headed back toward stability, the third note, a somewhat stable note, propels us towards "home" at the downbeat of the next cycle.
...and there you have it. The cycle begins again, and people dance!
Of course, there are other rhythmic structures that destabilize. Various types of claves (Rumba, son, African 6/8 clave), West African, Indian, and Middle Eastern rhythms contain cycling patterns of upbeat and downbeat emphases, and are delightfully destabilizing.
What rhythms DO NOT destabilize? Though 3-3-2 patterns are often present in rock music (i.e. the bass and guitar strumming rhythm on R.E.M.'s Man On The Moon), the music is usually firmly grounded by the kick drum on the downbeat, and especially by the backbeat on the snare drum. For this reason, even though it's some of my favorite music, I tend to find rock music and rock drum beats to be very stabilizing, and not very inspiring, propulsive in the dance studio, but maybe I just haven't worked out how to make it work yet, and it's actually a treasure trove of dance-inspiring sounds!
*You'll notice I don't use European music notation. There are a few reasons for this. European music notation is a very effective shorthand, useful for getting a musician to play a very specific thing. The 3-3-2 or "long, long, short" pattern can come in all kinds of rhythmic flavors, (swung, straight, something in between, uneven, etc.), many of which would not be represented accurately by two dotted eighth notes and an eighth note. Additionally, not everybody reading this knows how to read European musical notation, and the improvised music that I play in the dance studio has more in common with musical styles that have the body or voice as the point of origin, rather than an idea or the written symbol (a shorthand) used to represent it.