Introduction

When thou commandest me to sing it seems that my heart would break with pride; and I look to thy face, and tears come to my eyes. All that is harsh and dissonant in my life melts into one sweet harmony—and my adoration spreads wings like a glad bird on its flight across the sea.
I know thou takest pleasure in my singing. I know that only as a singer I come before thy presence. I touch by the edge of the far spreading wing of my song thy feet which I could never aspire to reach.
Drunk with the joy of singing I forget myself and call thee friend who art my lord.
Rabindranath Tagore
A lake. Still water. 
A stone is thrown into it, and the ripples spread.
Outward they go, in their patient circles.
Take two stones, and throw them together. And here, where the ripples meet: collisions, interference, little peaks and troughs that belong to neither ripple alone but arise, unbidden, from the encounter between them. The surface, which had seemed so settled in its patterns, reveals itself to be capable of something altogether more surprising. Two stones have produced what no single stone ever could.
Now, in a small effort of imagination, suppose the lake were not a lake at all, but the body of a violin, writ lake-sized. Vast, curved, its great arching plates stretching away in every direction, and somewhere in its surface, two f-holes open.
Throw your stones now. The ripples, which had previously enjoyed unlimited freedom of movement, find themselves in conversation with the walls. They bounce back. They meet themselves coming the other way. They jostle at the f-holes, squeeze through, and emerge into the air outside as something changed: shaped, coloured, given character by the particular contours of the vessel through which they have passed. The lake has become, in short, an instrument.
The stone, on impact, has not finished its business. It did not travel all that way merely to disturb the surface and consider its work complete. As it sinks (slowly, turning, as stones do) it continues to push the water aside, sending fresh motion upward and outward from the deep. What you see on the surface is only part of the story. The rest of it is happening below, where no one is watching.
Your body is the lake. Your breath is the stone. And the shape of the water… well. That, as it turns out, is entirely up to you.