What kinds of natural processes can be regarded as computations?

This chapter is concerned with how computational ideas can be used as the basis for understanding biological systems, not by simulating such systems, but by taking a computational stance towards the way such systems work. A number of issues are addressed. Firstly the question of what kinds of computer science are needed to help understand computational processes which happen outside of conventional computing machines. The second issue addressed places computational constraints on how the world can act into Dennett's framework of grades of possibility. The final main section considers the issue of changes in the world, and when it is meaningful to regard such changes as carrying out computations.