Many concepts are inadequate for serious inquiry, so theorists often seek to engineer new concepts. The method of explication, which involves replacing concepts with more fruitful alternatives, is a model of this process. In this paper, I develop an account of fruitfulness, the Relevant-Goals Account of Fruitfulness. The account is in the spirit of extant proposals, but develops and extends them in important ways. In particular, while it applies to explications in general, the account allows us to derive substantive details (...) for specific explications. This is achieved through a supplementary view, Contextualism, that specifies which theoretical goals are relevant in any given case. I close by discussing how the Relevant-Goals Account fits into the dynamic nature of inquiry. (shrink)