One of the most obvious features that characterises any technology is its in-betweeness. Suppose you live in Rio de Janeiro, not in Oxford. A hat is a technology between you and the sunshine. A pair of sandals is a technology between you and the beach on which you are walking. And a pair of sunglasses is between you and the bright light that surrounds you. The point may be phrased slightly differently, in terms of what exactly a specific technology relates. Perhaps a pair of sandals relates not you, but just your feet, and not to the beach, but just to some of its sandy surface. Yet this is hair-splitting and, in its essence, the idea of such an in-betweeness seems clear and uncontroversial. However, it soon gets complicated.