Creating parts that allow for rational design: Synthetic biology and the problem of context-sensitivity

•Biological engineering has to address context-sensitivity of biological entities.•Thinking of ‘parts’ and their ‘properties’ does not help to tackle context issue.•Potential alternative: biological entities as ‘capacities’ with condition spaces.•Cummins’ account of functional analysis is used to develop a capacity-based view.•This new perspective allows to explain successes in the parts-based approach.

The parts-based engineering approach in synthetic biology aims to create pre-characterised biological parts that can be used for the rational design of novel functional systems. Given the context-sensitivity of biological entities, a key question synthetic biologists have to address is what properties these parts should have so that they give a predictable output even when they are used in different contexts. In the first part of this paper I will analyse some of the answers that synthetic biologists have given to this question and claim that the focus of these answers on parts and their properties does not allow us to tackle the problem of context-sensitivity. In the second part of the paper, I will argue that we might have to abandon the notions of parts and their properties in order to understand how independence in biology could be achieved. Using Robert Cummins’ account of functional analysis, I will then develop the notion of a capacity and its condition space and show how these notions can help to tackle the problem of context-sensitivity in biology.