Rather, Galen insists, bodies (or substances) in the natural world have distinct capacities; in particular, there are four such capacities shared by all plant and animal bodies, the actions of which account for biological functions such as nutrition in a way which Atomist or mechanist views cannot. These capacities are: attractive, retentive, alterative, expulsive (e.g., Nat. Fac. III.4–8; UP IV.7; Temp. III.1, 269–70).