Closure has been described as a process which realises material and texture and which in successive layers provides the elements of experience, thereby determining our thought, and our social interaction. In the case of biological systems the function of closure however is not to realise material or provide experience but to intervene in openness. If, to use an earlier example, we have realised a face in the dots, the combined outcome of sensory and linguistic closure, we can find the face again, or cut it out, reproduce it, modify it. In the absence of the closure these interventions would not be possible. The interventions could occur in a physical sense, but if they were to occur they would do so as if by accident. A stone falling down a hillside can be considered to intervene in openness, but the manner in which it does so is passive: the stone is lost to the flux of openness. Moreover to imagine the stone intervening in openness is already to have imposed closure, for of course the stone in the absence of closure is not identifiable as a thing. Closure through the provision of material enables the system whether biological or mechanical to respond on the basis of the realised material and thus to intervene to achieve a particular outcome.