This chapter explores functionalism and structuralism in biology. A long-standing metaphysical dispute about the natural world is the ‘function-structure’ dispute: it concerns whether in the biological world function is prior to structure, or structure prior to function. This dispute can be interpreted as a dispute between rival metaphysical stances. These stances approach the natural world in a certain way, from a certain perspective, with a tendency to focus on, emphasise, and find meaning and significance in certain features, and de-emphasise others. This interpretation can explain the continuity of this opposition across radical shifts in scientific theory. The dispute predates the Darwinian revolution, for instance: there are pre-Darwinian functionalists and structuralists, and evolutionary functionalists and structuralists. The pre-Darwinian and evolutionary functionalists (structuralists) held very different beliefs and theories, but were philosophically united in terms of a shared metaphysical stance. This is an example of the way in which the construal of metaphysical positions as stances allows the empiricist in particular to accept that metaphysical assumptions and presuppositions have an important epistemic function in scientific practice, while honouring empiricist scruples about traditional metaphysics. But one need not be an empiricist to accept the arguments I present.