“Imagine you are studying the migratory patterns of a certain species of bird. Although we see them soaring and wheeling like free spirits – ‘free as a bird’, we say – they are subtly tethered to the earth. They have freedom to go where they want, it is true, but within certain constraints that are dictated by the realities of their embodied being. To understand a bird’s migratory patterns would require knowing something about the landscapes over which it flies – the opportunities for food and shelter they afford, the weather patterns they give rise to, and so on. These facts would not ‘cause’ the migration, still less are they themselves the migration, nor could they ‘explain it away’: they would simply indicate the constraints on the migration, that helped account for the pattern it tended to take. Sometimes, for contingent, or no discernible, reasons, a bird or birds might vary the pattern considerably and end up in Iceland instead of Scotland. But generally there would be a familiar shape to it, understandable in terms of the whole context: the nature of the land, sea, weather, fauna and flora through and over which the migration route passes.”