Reductionism isn't Functional

holism versus reductionism, process algebra, object orientated programming, philosophy of biology One of the great current debates in biology concerns whether the observed behaviour of a system can be accounted for in terms of the behaviours of its subcomponents. The problem is often presented as a question of ‘holism versus reductionism’; whether ‘the whole is greater than the sum of its parts’. The holist position is that biological systems display certain phenomena that cannot be understood by thinking about the system at any lower level than its entirety; reductionists argue that systems can be explained completely in terms of their subcomponents. We show that de Simone's theorem, a result derived in a relation of Professor Robin Milner (FRS)'s Turing Award winning work in concurrency theory (a branch of theoretical computer science) provides an answer to this problem. De Simone's theorem proves that all possible systems can be reasoned about in terms of their subcomponents. Hence, if the parts of systems are represented as processes with internal state rather than functions, it is always possible to explain system behaviour in terms of the interactions between its parts.