 A functional explanation is one in which something that has an effect, is explained in terms of its effect. Cohen often uses an example from evolutionary biology to illustrate this; namely, that “birds have hollow bones because hollow bones facilitate flight”. Here, something (birds having hollow bones) which has a certain effect (facilitating flight) is explained by the fact that it has that effect (“birds have hollow bones because hollow bones facilitate flight”; G. Cohen 1988: 8). In short, where e is a cause and f is its effect, functional explanations maintain that: e occurred because it would cause f. Or, more properly, functional explanations maintain that: e occurred because the situation was such that an event like e would cause an event like f (G. Cohen 1988: 8).