Abstract: Conceptual engineering is the process of assessing and improving our conceptual repertoire. Some authors have claimed that introducing or revising concepts through conceptual engineering can go as far as expanding the realm of thinkable thoughts and thus enable us to form beliefs, hypotheses, wishes or desires that we are currently unable to form. As exciting as this idea certainly is, it has never been developed or defended properly. In this talk, we pursue a twofold goal. First, to offer a theory of what such mind-expanding conceptual engineering is and what distinguishes it from other kinds of conceptual engineering; second, to show that this kind of conceptual engineering is possible, both in theory and in practice, and to explain how it can be pursued. A central starting point for the account is Susan Carey’s work on conceptual discontinuities and Quinean bootstrapping.