Movement 1: Hairless crash test dummies, simple models of the human body and the magic of its 'centre'

Before proeeding into a nuts-and-bolts explanation of how and why maximum mutual predictability gives rise to good dancing, it is necessary to discuss what is meant by a dancer's 'centre', and why it is important. The goal of this post is to introduce the idea that a complicated physical system, like a pair of people dancing, can be effectively represented by a simple model. This simple model is useful because it is easier to understand than the real system and can be used to gain insight into what makes the complex, real system tick. I will argue that in the case of a dancer partnership, the motion of each partner can be adequately represented by the motion of his/her 'centre', or centre of mass.

In later posts, we will gradually put together a simple model, which I believe effectively represents good partner dancing. If we just launched straight into the model now, it might not be clear where that model came from or why it works, and that might be annoying. So, at this point, it will be useful to first describe the general process of creating an effective simple model for a complicated physical system - like a connected pair of dancing human bodies. We will take a brief step away from dancing and just talk simple physics for a moment to get a feel for the big picture of how we will look at dancing afterwards. Doing this now will help things to make sense as we proceed further down the track. Please don't worry if you've never studied, or even liked, physics. I will do my best to make this as painless as possible. I promise there won't be any equations, at least not yet ;-)

Physics is mostly about describing fundamental relationships in the natural world. The practical process of how this is done usually proceeds something like the following. We will consider a practical example throughout, to help it all make sense. This example - that of using crash test dummies to understand how human bodies move during traffic accidents - might seem a bit gruesome but I have chosen it because it deals essentially with the same question we are facing in trying to model good dancing: How simple can I afford to pretend that a human body is so that I can study its behaviour more easily? Do I need to study a perfectly lifelike model, with all the detailed features of the human body, like hair length, eye colour, etc, or can I get away with studying a simpler model like a 'stick figure', which lacks all these details but still has all the important bits? The process by which we usually answer this question in physics goes like this:

Step 1) Observe something interesting in the world and wonder about how it works - how all the parts relate to each other.

Let's begin our example in an historical context. In the early days of automotive transport, cars were engineered to transport people and stuff, without a lot of consideration for keeping all that stuff safe in the event of an accident. Over time, as more and more people got hurt in car accidents, patterns were identified in the kinds of injuries that resulted. This posed a question - why do these kinds of injuries happen in car accidents, and how can cars be better engineered to prevent them from happening in future?

2) Based on your experience of how things have worked in other parts of nature you're familiar with, identify the essential features of this new system and, for simplicity, temporarily forget about all the stuff you think is probably non-essential.

What are the features of a person's body, which most strongly determine his/her injury risks in a car accident? Based on past experience, you might assume that body mass, size and approximate shape, for example, are more important than hair colour or length of fingernails.

3) Put together a simplified model (often called a 'toy model') in which the system of interest is composed only of the features you have decided are likely to be essential. This is usually done first in one's head and then in diagrams.

I am not familiar with the actual historical process of how car manufacturers went about modelling car accidents and how that progressed over time, but I know that it eventually resulted in sophisticated experimental tests using the iconic (and hairless) crash test dummies that have become familiar to the public. Presumably, things started much simpler than that. The very first crash tests might have just had human-weight bags of sand on the seats, for example. Early theoretical models might have been very simple, just representing a person's body with a simple shape - maybe a sphere or a square-edged box - with the same mass and roughly the same size (so, the same density) as the average human body. It's always easier to start with a very simple model and add in complexity in small steps from once the simple model is understood.

4) Using fundamental laws of nature and mathematics, derive equations that describe the dynamics of your toy model.

If we assume, as speculated above, that a simple model of a human body might be a spherical blob with the same mass as the average human body, then for this step of the process, we would use the laws of Newtonian mechanics (originally formulated by Sir Isaac Newton in the 17th century and still used today for describing how physical objects behave on the everyday size and time scales familiar to humans; ie. not very small like atoms or very big like galaxies, but in between like people in cars) to write down equations describing the behaviour a spherical person in a car accident. These equations are usually then used to generate graphs or computer simulations, which allow for the visualisation of how the toy model is behaving.

5) Compare the behaviour of your toy model to the behaviour of the real system you are trying to describe and note how different they are.

Our spherical person model would probably do a good job of describing the behaviour of a person's body overall but would tell us nothing about the detailed movements of limbs.

6) Revise the toy model, adding in some complexity.

We might add some sticks to our sphere so that the toy model now looks roughly like a body with simplified arms and legs.

7) Repeat 4-6 until the model's dynamics are deemed to be sufficiently like the dynamics of the real system.

We can speculate that over time, this gradual iterative process resulted in the crash test dummies that we have today, which are clearly a lot more like real people than is a spherical blob. However, importantly, these dummies still don't have hair, eyes, individual fingers or toes, or other such details, presumably because it has been decided along the way that including these details complicate things without helping to answer any imporant questions about car safety. Eventually, a point of diminishing returns is always reached at which adding more details to the model makes the science a lot harder without significantly adding to the descriptive power of the model.

Ok, strict physics talk over for now. Phew! Let's get back to talking about dancing! The question I'd like to address in this blog is, 'Is it possible to come up with a simple model, which describes the essential features of good, musical, improvisational partnered dancing, and can the nuts and bolts of that model be used to develop practical tools for improving people's dancing?' I think the answer is yes and I will attempt to show how and why.

In our crash test dummy example above, the very simple model we started out with for a person's body was a spherical blob that weighed as much as the average person. It turns out that we could have started with an even simpler model. Before representing the person with a 3D spherical blob, we could started with a 1D blob, called a 'point mass'. We would prented that all the person's mass were concentrated at a point in space and we would locate that point at the real person's centre of mass (COM). So, we would be replacing the person with a microscopic (actually, infinitely small) marble, hovering in space at the centre of where the real person used to be. Despite being tiny, this marble would weigh the same as the person. This is arguably the simplest possible way to represent a 3D object. I will argue that for modelling dancing, this very simplest of models is adequate for practical purposes. We won't even have to make things as 'complicated' as to pretend that a person is a spherical blob. Instead, we will be able to imagine that a person is simply a single point in space, like a tiny marble that weighs as much as the person it represents.

In my experience, most people have some concept of what their COM is but we need to make sure we're clear here, so let's talk for a moment about what, exactly, we mean by COM. Your COM is the average position of all the mass in your body. Your COM changes as you make different shapes with your body, and it can even be outside of your body. For example, if you're standing up and you bend over to touch your toes, your body (seen from the side) is making a kind of triangle shape and your COM will be somewhere inside that triangle. Since your torso is probably heavier than your arms and legs, your COM will be closer to your torso than your feet. Nonetheless, it is probably outside of your torso, hovering in space just below your ribcage somewhere. When you stand back up again, as your body comes to form a vertical line, your COM will sneak back inside your torso, probably just behind your bellybutton. It is important to understand here that your COM is not a physical object, it is just a number calculated from the positions and masses of all the real parts of your body.

Even though the average position of all the mass in your body is just a number, not a real object, it is very useful because it is the fairest way to answer the question, "Where is my body?" with just a single point in space. If someone wanted to know where you are located in a dark room, giving them the coordinates of your little toe does not very fairly represent the position of your body, because most of your body is located to one side of that point. But reporting the position of your belly button gives a much more useful piece of information because (assuming you are standing straight), it is close to the average position of all of the mass in your body; your mass is located all around it so anyone aiming for that point is likely to find you even if they miss in any direction.

I'd now like to demonstrate the usefulness of the COM in tracking a dancer's movement. Imagine that you are given three videos of a dancer dancing in a dark room. In the first video, the dancer wears a glow-in-the-dark dot on one of her hands and all you are able to see in the video is the motion of the dot, which darts all over the place. In the second video, a similar dot has been attached over the dancer's belly button. This dot moves more smoothly and covers less distance than did the dot in the first video. The last video was shot with a 'night vision' camera, so you are able to see the dancer's whole body. You notice that the overall quality of the dance, when the whole body is considered together, is more like the motion of the belly button dot than the hand dot. This is because the dancer's COM will never be far from her belly button and the dynamics of her COM are the best single-point representation of her whole body's dynamics. Her hand, by comparison, will spend most of its time far away from the dancer's COM and so moves in a way that is unrepresentative of her whole body's motion.

Swing dancers are often taught to 'move through your centre' and leaders are taught to 'lead with your centre'. The reason for this, I believe, is that a dancer's centre (COM) is, speaking in strict physical terms, the heart of their 'identity' as a physical object. When I am dancing and connecting with my partner, the best way for her to know what I am doing is for me to communicate to her what my centre is doing. The rest is details and those details are easy to lose when the very task of sharing control over the dance partnership is so difficult from the start. The business of movement and connection then, is about doing so in ways that clearly communicate to your partner what your centre is doing. As we will see in more detail in the next post, making your centre's movement predictable for your partner will make it easier for him/her to cooperate with you in co-creating the dance.

One final note should be added to this post. Modeling a dancer as his/her COM is the simplest possible model one can construct and in some circumstances, a slightly more detailed model is useful to consider. One can construct an arbitrarily complex model by combining COM models for components of a dancer's body. The next step up from the basic COM model is a model in which the dancer's body is considered in two halves - upper (from the waist up) and lower (from the waist down). Each of these halves has its own centre of mass; we might call these the 'upper centre' and 'lower centre'. As we will see later, breaking things into two parts like this is particularly useful when considering the connection required to lead and follow turns. From this point, we might take the next step up in complexity and explanatory power by breaking the body into six or seven pieces: the torso (in the six piece model; in the seven-piece, the torso would be split into upper and lower torsos), the four limbs and the head. Note, a three-piece model could also be constructed, and would be the next logical step from a mathematical perspective, but the six-piece model makes more sense from an anatomical perspective. This process can be carried as far as we like, with pieces being broken into ever smaller pieces which are modelled as their centres of mass, until a model is created, which is sufficiently accurate to answer whatever question one might be considering. For most practical questions however - the kinds of questions which might help teachers teach and students learn practically - a basic COM model is adequate.

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Moving and connecting as nature never intended

Most readers will be familiar with Windows Media Player's (WMP) music visualisation programs, which splash weird, eye-catching images across the screen, changing in real time to reflect musical dynamics. These might look pretty but they do a lousy job of representing music. If you watched one with the sound muted, how much could you infer about the music? My guess is, maybe some rhythms at best. Dynamic visual representation of music is not easy.

You can dance better than this.

Now consider this: WMP makes its visualisations using just a single computer. The flow of information is simple:

Music --> Interpretation by a single computer --> Visual ouput, one frame at a time.

This is not all that different from what a solo dancer needs do to be musical. The dancer's visual canvas - his body - is controlled by a single brain. Music is heard and interpreted, musical movements are planned and executed. Obviously this is a simplification of the complex physiology at work but the point is, dancing within one body doesn't ask for anything outside the range of normal human behaviour. Millions of years of evolution and a lifetime of experience have trained your brain to hear music and move your body in all kinds of amazing, finely controllable ways, which are readily adaptable to environmental demands like swingin' tunes.

Why is well-connected, flowing partner dancing so difficult? There are lots of reasons of course, but many of them stem from one fact: a single dynamical system (two human bodies trying to dance together as one) is being controlled by two brains, each with its own ways of interpreting music, and has direct sensory and motor connection to only one half of the system. That is, your brain, via your nerves and muscles, can only directly control the half of the dance partnership that is your own body. And yet somehow, the two parts are supposed to closely cooperate to artistically express, adaptively in real time, some compromise between your two different interpretations of the music. It seems impossible! And yet the best dancers can do it well. How can this be?

Over the years, dancers have evolved - culturally, not biologically - systems of movement and connection, that afford them a high level of shared body control. These systems work by constraining the movement options of each individual partner so as to give the whole partnership more options. Not unlike in most relationships between life partners, each dance partner agrees to not do certain things so that the partnership might be able to do more. Later posts will deal with the mechanical details of these self/shared control systems. The rest of this post will describe the guiding principles behind them.




The first principle is that these systems are primarily functional. They are not the way they are because some authority figure in the past said that people must move and connect in certain ways. Rather, these systems evolved for the same reason that all complex things have evolved: they succeeded where others failed. Many dancers, dancing many dances, for many years, through trial and error have developed efficient systems of movement and connection. These allow for a high level of fun and creativity with the least effort on the social dance floor. Interestingly, it has not been necessary to deeply understand why these systems work; for practical purposes, knowing and teaching the how is enough.

So, on to practical matters! As far as I can tell, the main guiding principle behind effective movement and connection is mutual predictability. Each partner needs to move and connect in ways which make it as easy as possible for the other partner to have the experience, "Ahh, I see and feel what you're doing and where you're going with that. I can work with that!" Of course, too much of anything is a bad thing; if you move too predictably (eg. doing the same 'move' over and over), your partner will get bored. A balance must be struck; it's all about time scale: predictability over a few seconds is good, a few minutes, not so good. Perhaps a better word than 'predictability' is 'trackability'; your partner must be able to track what you're doing. But, for the sake of continuity, let's stick with 'predictability'.

Before moving on though, one other point must be made about this word. Reading the word 'predictability' might be setting off alarm bells for you because teachers often stress, to followers in particular, that prediction/anticipation of leads is a no-no. I agree with this. This is different from the kind of prediction I'm talking about. This kind, the kind to be avoided, is less about prediction your partner's movement and more about assuming that you're capable of reading his/her mind. This is sure to lead to dysfunctional dancing because often, not even the leader knows what he/she is thinking; advanced leaders frequently just let the dance unfold and 'go with the flow', often without strict plans for what will come next. Good followers learn how to keep track of their leader's 'flow' (trajectory) without making any assumptions about what that means for the follower. There is no 'supposed to do' in pure following; there is only letting the dance be done to you. If it is not done to you - if your motion is not physically changed for you by energy provided by your leader, with zero extra energy input from yourself (which is a functional definition of pure following) - then whether or not it was intended doesn't matter. Of course, good followers have a huge amount of input into how they are dancing, but they accept that input as their responsibility; it is not an attempt to guess what the leader might be thinking. In summary then, what I am advocating is promoting each partner's ability to track what their partner is doing within their own body, identify a pattern and see where it is likely to lead, without inferring that some particular response is required (that is the kind of 'anticipation' that should be avoided.) If one can avoid feeling obliged to lead oneself in response to something that one's partner has done with his/her body, then prediction is a useful thing because it provides a reference point for one's own self-directed dancing within the bounds of the partnership.

If you can see that your partner is moving is such and such a way and predict where that will take him/her over the next few seconds then you can plan around that in a way that allows you dance with enough independence to have your own fun while always being ready to pass energy back and forth (lead/follow) with your partner. A simple example of this is a good old footwork variation. A good leader will move and connect in a way that usually allows his/her follower to know when has been given enough 'space' to add in a variation without interupting the flow of the partnership. An inexperienced lead, by contrast, will be harder to track and prone to giving the follower the impression that she/he can never quite know what's coming next so it might be unwise to do anything but strictly follow. Of course, predictions can always be wrong, even between the best dancers. What I am arguing is that in general if partner (A) moves and connects in such a way that partner (B) can be reasonably successful is predicting (A)'s dancing into the near future, then (B) will be in a better position to cooperate with (A). (B) should also try to allow the same kind of predictability for (A). A useful analogy here is a squadron of jets flying together. If the squadron is to stay together without constant radio communication ("Ok guys, we're all about to slowly peel left. You ready?"), then each jet must fly in a way that is predictable to the others. There are certain simple, physical rules (like 'no sudden moves', for example) which allow this to be achieved. We will look at these rules in detail in future posts.

I'd like to finish this post with a brief discussion of lead and follow. Splitting a partnership into lead and follow is, of course, the one big pre-agreement that has to be made between the two brains controlling the two bodies in the dance partnership if anything at all is going to be achieved cooperatively. The agreement is simply this: When one partner is passing energy to the other ('leading'), the second partner will allow that energy to flow naturally into their body and be conserved in the process, meaning that it will usually change the way that they are moving. Note that no mention is made here of one person being the leader and the other, the follower. The best dancers will tell you that both partners are both leading and following throughout most dances. A good dance is a conversation, with two speakers and two listeners, not a monologue with one of each. The only restriction is that, just as in a good conversation, the two partners do not try to talk over the top of each other. When one speaks (leads/gives energy), the other listens (follows/accepts energy). Strictly speaking, I believe it is physically possible to both lead and follow at the same time; it's just extremely difficult and not really necessary for the creation of fun dancing.

I suppose that special mention should be made here of historical exceptions. Blues is probably the most conversational of the usual swing-associated styles. I'd say Lindy hop comes in at second place. Balboa, on the other hand, is more traditional and many people feel strongly that is should be role-based as far as lead and follow are concerned. That is, one person leads for the whole dance, the other person follows. End of story. This is a cultural contraint, however, not a functional one. Speaking in strictly physical terms, lead and follow can be shared back and forth in any partner dance. Doing so will make some things possible, which are not possible if the lead is uni-directional. At the same time, it will make other things harder. Presumably, the Balboa community has decided that the latter is too great a cost to justify the former. For whatever reason, Blues and Lindy have evolved into dances, which allow for lead-sharing whereas Bal, in general, has not. I am not trying to argue that one is better than the other, only that they are different. Cultural constraints aside, the same general physical processes are at work during leading and following in all of these dances. In future posts, I will attempt to explain in detail, the mechanics of pure leading, pure following and lead-sharing.

In this post I have tried to demonstrate that musical, co-creative partner dancing presents a challenging shared control problem. I have argued that systems of movement and connection have evolved, which allow for efficient shared control within a dance partnership, and that this is achieved through mutual predictability between partners. Finally, I have argued that control can be shared in different ways through different systems of leading and following.

In coming posts, I will further explain the notion predictability in movement and give it a clear physical definition. I will then attempt the explain the system of individual movement, which I believe good dancers use to make their motion predictable to their partners, to facilitate good connection.

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Painting jazz

Let's carry on with the definition of musicality from the last post:

Musicality is achieved when a dance looks and/or feels like the music sounds.

As discussed, humans may have evolved an in-built system for associating sounds, shapes and movements. This system is shared across the population so people usually agree on what is musical dancing and what isn't.

I think there's something else to add here: The correspondence between sounds and dance shapes/movements is not one-to-one.

I don't believe that for any given sound, there is one and only one dance movement, which corresponds to the sound better than all other possible movements. There is always some fuzziness, an array of options, all of which will fulfill the inbuilt human assesment criteria for musicality. At least, I have no idea how one could quantify one-to-one correspondences if they did exist. It may even be impossible, if, say, the neural mechanism for these associations makes them based only on coarse properties of the motion and is incapable of selecting between finer details. For example, maybe a quick blast on a trumpet corresponds to a quick movement in some part of a dancer's body, but exactly which part moves might not matter; so long as it's fast, any movement might look equally musical.

Consensus and individuality

I think this is good news because it leaves room for individuality in musical interpretation. Everybody - and every body - is different, each with it's own particular physical constants and predispositions. Similarly, each person's experience with music throughout their lives will have shaped how they hear and interpret music. I believe that the first step for each dancer in finding her own style is to focus on her own natural process for hearing music, extracting its various features and translating them into body movements, which feel natural and musical. In my classes I teach exercises to facilitate this. My experience in these workshops is that ten different dancers will come up with ten different ways to dance one sound but they will usually all look musical. My favourite part of teaching this material is looking around the room and seeing the joy that people get from appreciating the diversity in each other's musical interpretation while also feeling connected through broad agreement. I sometimes get the impression that people feel like they've just discovered that they can speak to each other in a language they never knew existed. For reasons outlined in the previous post, this may in a sense be literally true.

With this is mind, I would like to discuss something. I think there's a mismatch between how most dance teaching is done and the goal that most dancers are aiming for (consciously or unconsciously). I've taken hundreds of dance classes over the years, maybe more than a thousand. And from all those, I think I have enough fingers to count the classes that weren't based on routines of moves. Moves themselves are really just small routines of movements, and moves are linked together to make larger routines. So, from here on, by 'routine' or 'move' I will refer generally to pre-defined patterns - programs - of movement. Of course, good teachers also emphasise the importance of technique and musicality. So it is natural to ask, does learning routines help to develop a dancer's technique and musicality? Are we doing the best job we can do as teachers by focusing on moves?

Shapes and tools

I would like to make a visual analogy here. Every move is like a pre-made, cut-out image. It hangs together in and of itself but it has no background, no context. Imagine now, that like a happy little kid, you are sat down at a table with a long strip of blank paper, a few dozen pre-cut images and some glue. An inspiring piece of jazz music is played to you and you are asked to visually represent your experience of the music by gluing the shapes onto the paper strip in sequence. Your options are only as many as the various permutations of the shapes at your disposal. Rearranging moves in never going to fully represent the beautiful complexity of a person's musical experience.

The dancer would be more empowered if, instead of being given ever more precut images in each class, she were taught how to paint. That is, given a few simple tools - the most basic elements of movement - and then taught the mechanical rules for using those tools to create his/her own original images, extended, flowing and continuous, without breaks or joins, created from moment to moment, directly inspired by the music.

Of course, in the early stages of learning, precut images are useful and are perhaps the best that the learning artist can hope to achieve with the paintbrush while mastering its flow (this is analogous to dancing through a pre-defined move using genuine lead/follow connection and efficient movement). But the goal is to leave all this behind once painting is comfortable. Painting jazz well can only be done spontaneously, improvisationally, from moment to moment, without knowing exactly what the next moment will bring.

In coming posts, I will attempt a course in jazz painting. It will begin with an introduction to the physical principles of good dance moment and proceed to the principles of functional connection between dancer partners. That is, mechanical principles that allow for flowing co-creation of musical dancing. For anyone who's ever struggled with the essence of what the best dancers do when they move and connect, things are, I hope, about to get interesting.

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What is musicality?

Let's try this on as a simple, working definition: A dance is musical when it looks and feels like the music sounds. But how can a look or a feeling be like a sound? I don't have a complete answer to this and, as far as I know, no one else does yet either. But let's discuss some clues.

Sights are sounds: Synesthesia

There is a fascinating phenomenon called synesthesia, which is well studied in perceptual psychology. Synesthesia is a cross-over between senses (sight, hearing, taste...), in which particular experiences from one sense are accompanied by experiences from another sense. For example, a synesthete (a person with synesthesia) may see the colour red when hearing a middle C. An E might be green, a D blue, and so on. Synthesesia comes in all shapes and sizes and sometimes produces strange effects within a single sense; a synesthete friend of mine once told me that she always sees particular letters and numbers in particular colours, regardless of the colour of the text she's looking at (though she's also able to see that colour too; she's conscious of both at once). So, the number 1, for example, is always experienced as yellow, even if the font colour is black. A famous example is an incident in which an accomplished composer/musician visited a tailor and ordered 'a suit in the key of C major'.

Last I read about the subject -- some years ago now -- the prevailing brain science explanation for synesthesia was that neurons in the parts of the brain that deal with different senses would establish connections with each other, which don't exist in most people's brains. These connections would allow the neurons to 'talk' to each other, producing effects that most people don't experience. As it happens, all these regions are located nearby to each other (the whole cluster is called the sensory cortex) in an area at the top of your head, about half way along, called the parietal lobe. This proximity means it's easy for connections to form between visual and auditory neurons, for example. When particular visual neurons fire they might cause connected auditory neurons to fire, and this causes an auditory experience to accompany the visual experience.

Synesthesia is a clear demonstration of natural overlaps between experiences in different senses but it doesn't happen to everyone; it is a 'disorder' affecting a small minority. On the other hand, musicality in dancing seems to be recognisable to everyone. How can we account for this?

Musicality as a quirk of language evolution

Language is among the most intensely studied fields in psychology. It has been argued that humans, uniquely among animals, have an innate capacity for complex language with properties like grammar (Read Stephen Pinker or Noam Chomsky if you want to look into this). It is thought that there are universal laws underlying the grammatical structures in different languages (that is, universal rules about how the specific rules arise). By this theory, the most basic laws of language are hereditary, and these are applied as a child learns particular languages provided by his/her environment.

There are various ideas about how this 'language instinct' evolved in humans. Some authors, like Pinker, argue that language was itself an adaptive trait (it helped our ancient ancestors to survive and reproduce by improving their ability to communicate and work together) and evolved through natural selection. Others, like Chomsky, argue that language appeared as a byproduct of other adaptations. Both of these positions -- the former in particular -- are faced with the challenge of explaining the process of language evolution. What primitive communication strategies came before the complex
languages that eventually evolved? As far as I know, there are a number of competing theories about these early communication systems but I'd like to focus one popular one: that gesture -- visual and tactile language -- was one such early strategy, and verbal/auditory language was gradually added to systems of gestural communication before evolving to dominate them. This resulted in the verbal language systems we have today, where talking/listening is primary and gesture plays a lesser but important part.

By now you might be wondering, what does all this have to do with musicality in dance? Current theories in the psychology of music (see for example, Daniel Levitin's book, 'This is your brain on music') hold that humans' unique capacity for music production and appreciation are a by-product of our unique, evolved capacity for language. Music and language share many fundamental features. Both exploit tone, rhythm, pitch, pause, etc. It can even be shown that the structures in music obey grammatical laws, partly innate and partly culturally defined, just like in language (see Levitin's book).

Echoes of early language evolution can still be seen in the way that people communicate today. Gesture is still a natural part of verbal communication. It might be tempting to write this off as coincidence but there is compelling evidence for a deep, innate capacity for association between visual shapes and sounds. In 1929, the German-American psychologist, Wolfgang Koehler did an experiment in which participants were shown the following two shapes,


and asked which assignment of the two names 'Bouba' and 'Kiki' seemed most natural to them, based only on the sounds of the names and the appearance of the shapes. There was 98% agreement that the shape on the left is the Kiki and the one on the right, the Bouba. 98%! The explanation for this result remains controversial but prevailing theories are based on the above-explained connection between shape and sound, that evolved for communication purposes.

Given that current theories about music psychology trace the roots of music to language evolution, it seems reasonable that the echoes of early language evolution should also be seen in how people interpret and communicate music. We might expect that there should be natural, innate associations between musical sounds and gestures, the latter being made up of shapes and movements. And, importantly, those associations should be shared throughout the population. It is not hard to see how a natural theory of dance musicality emerges from these ideas. Anyone who has ever been to a dance contest and listened to the cheering will know that the crowd tends to agree when the competitors do something particularly musical! This recognition applies not just to momentary shapes but also to whole trajectories of dance. A sequence of tone-matching shapes, strung together through movements that match the musical dynamics and end in a visual full-stop coinciding with a 'break' in the music seem to exemplify innate associations between sounds, shapes, motions, and overall grammatical structure.

This is musicality; a delicious remnant of our evolutionary past.

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Stating the problem: What the heck is 'swing dancing' anyway?

A favourite quotation of mine comes from the jazz critic, Garry Giddins who features in Ken Burns' 'Jazz' documentary series:

"[Jazz] is the ultimate in rugged individualism. It's going out there on that stage and saying, 'It doesn't matter how anybody else did it. This is the way that I'm going to do it.'"

And another, from the great Duke Ellington:

"Put it this way. Jazz is a good barometer of freedom... In its beginnings, the United States of America spawned certain ideals of freedom and independence through which, eventually, jazz was evolved, and the music is so free that many people say it is the only unhampered, unhindered expression of complete freedom yet produced in the country."

The great irony of jazz is that its central tradition is innovation. The greatest jazz musicians and dancers, past and present, rose to fame not by doing what had been done before but by doing something new, their own way, stretching the frame provided by history. I'm not claiming that any old thing qualifies as jazz, provided it's different. I'm claiming that good jazz - both music and dance - is about putting a few new brushstrokes on the giant fresco, which has grown at the hands of many before you, rather than just going over the same old strokes again. I am no jazz connoisseur but I think there might be something in this idea as a guiding principle for getting to the heart of good jazz dancing. In my experience the most common definitions that people seem to have for 'swing dancing' are something like the following three:

1) History: 'Swing dancing' is an umbrella term for the various vernacular jazz dances of the original jazz era. The exact dates and dances included tend to be controversial but the general idea is understood. It follows that the highest goal of any modern would-be swing dancer should be to recreate the dancing that was done 'back in the day', tiny snippets of which can be watched in old videos.

2) Moves: This is an extension of 1). Swing dancing consists of a large list of predefined moves and routines, which have either been handed down from the original swing era or have been created since, 'in the spirit' of that era. According to this definition, a dancer's goal should be to learn and remember these patterns, as well as how to mix and connect them in ways which feel natural, look impressive and reflect whatever music is being danced to.

3) Rockstars: Good dancing is whatever is done by the people who win the most competitions and/or get the most teaching gigs. An aspiring dancer's goal should be to emulate the dancing done by those people.

Predictably perhaps, I think these definitions all miss the point because they focus on doing what someone else has already done; they forget the innovation. I think that all three of the above are kind of 'grades in swing school', phases that dancers progress through as they improve. But in order to graduate, a dancer has to move beyond these and find his/her own style.

But what does that mean?

Good dancers do what they do for all kinds of reasons. Sometimes it's about fancy moves or aerials, which are athletically difficult. Sometimes it's about dancing to the level of a partner, deliberately going easy so that a dance can be fun for someone of a lower skill level. Sometimes it's about being silly and not taking things too seriously, or it could be about taking things very seriously and trying to win competitions. The list goes on. But in my experience there's one universal across all these situations: No matter what the circumstances or goals, good dancing will be improved if it's also musical.

So, what is musicality? It seems to be something that is generally understood - everyone knows musical dancing when they see it - but difficult to break down and explain. So then, if this blog is to focus on picking apart in a scientific way the fundamentals of jazz dancing, this seems like a good place to start...

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The curse, the dance, the quest

All scientists know the curse of thinking too much. Maybe it's no coincidence that there are many scientists and geeks of all flavours in the swing dance community; dancing is a release from thought, a kind of meditation, musical yoga for two. For me, above all else, it's that experience of presentness, caught between a partner and the music, that keeps me coming back for more. I suspect I'm not alone.

But what about away from the dance floor? Swing dancing has a habit of sneaking into people's brains and setting up shop like some kind of syncopated fungus. No matter what your line of work, once it's in there there's no escape. You practise Charleston while you're waiting for your lunch to microwave, and while you're eating you think about practising Charleston. And think about it. And sacrifice your eyes on the altar of Youtube.

The improvisational partnered dances of the jazz era first staked their claim on my brain in 2000, when I was 17, and never left. As it happened, shortly after my first dance class I took my first class at university too. On my dance journey since then I have found my studies in physics and cognitive psychology particularly useful in understanding the dances I love. After all, what is partner dancing if not brain-controlled movement of connected bodies?

No matter where the lindy hop came from, no matter which snippet of history gets you fired up about what is and isn't blues dancing, and no matter which vintage video made you style your Bal the way you do, the laws of physics don't often concede an argument. There are simple facts about the ways bodies move and interact that quietly persevere no matter what storm of preference and politics is swirling around them.

Over the years, I've heard people say things like, "You can't capture the essence of this dance; it's too free!" and, "Lindy hop is one part physics, two parts creativity and three parts magic!" Maybe. Sure, I can appreciate where these people are coming from. When I swing out, I leave my calculator and pocket protector behind. I STFO 'cause it feels good and that feeling doesn't come from the mechanical bits and pieces of the dance, it comes from the blend; the magic lies in the whole enchilada. There are few things more joyful to me than the mindless flow of a dance that unfolds so naturally I feel like the music is playing my partner and I in unison.

There are no words for that. Right? I mean, could anyone ever wrap up that magic and dispense it in bite-sized chunks to eager-faced dance students? Well, call me crazy, but I think that the answer might just be yes.

There are only so many times that a physics student can hear his dance teachers talk about energy, momentum and stretch before he starts to read between the lines and see equations. There is only so much talk of musical interpretation and 'conversation' in the dance that a psychology student can hear before he wonders whether his brain's language centres are lighting up while he and his partner are arranging movements like words across a musical phrase. And there's only so far down the rabbit hole that a curious fellow can venture before wondering whether at the bottom there might be a grand unified theory of partnered jazz dancing waiting on a velvet cushion for anyone who bothers to look.

This isn't just about satisfying curiosity though. Figuring out 'the laws of partnered dance mechanics' can have practical results. My own dancing and teaching have improved a lot from beating my head against the question of what's actually, physically going on in the best dancers' bodies, and then trying to make those same things happen in my body. But I have also come to realise that understanding something and actually doing it are different. I could write a book on the mechanics of Kung Fu and still get my butt kicked by a grumpy grandma. Seeing my theories of movement and connection playing themselves out between the world's best lindy hoppers doesn't equip me to match them, no matter how hard I might wish.


So, why bother to write this blog? Well, the inverse is of course also true; great dancers don't have to understand what makes them great, they only have to do it. This mismatch can create a serious challenge when it comes to teaching. Please don't get me wrong; I respect the teachers who have devoted their lives to spreading the joy of dance and I'm all for fun, accessible teaching. I just want it to be grounded in reality. Giving students a physically accurate, self-consistent picture of how good dancing works helps with their learning. It just needs to be boiled down into fun, accessible teaching concepts. Fun and truth; that's what I want.

So, I'm interested in nailing down some truly universal rules about good dancing; rules that go deeper than touchy-feely analogies and vague allusions to energy, momentum, stretch, delay, etc. In the posts that follow, I'll share some ideas about whether and why such universal 'laws' might exist, and what they might be. Throughout, the goal is to focus on what works.

I will address these questions and more:

• What is musicality?
• What kind of body movement works in connected dancing and why does it work?
• What is a dancer's 'centre' and why is it so important?
• What is the relationship between steps and movement?
• Why is 'pulse' important?
• What is 'connection' between dance partners?
• What is 'frame', what essential properties allow it to work, and why?

I hope that there might be someone out there, who finds these ideas useful.

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