We take initial steps towards a meticulous analysis of functions (including the so-called "use function") within a recently proposed, unifying dispositional framework for realizable entities in Basic Formal Ontology (BFO). Our approach to function is strikingly characterized by an ontology of "extrinsic dispositions", which are realizable entities outside the BFO category of disposition. This work helps to articulate multiple possible senses of the term "function" within BFO and to deepen the understanding of the present BFO dispositional theory of function.