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. If true, this would allow conceptual engineers to contribute to solving stubborn problems – problems that cannot be solved with our current ways of thinking. We call this (...) kind of conceptual engineering heavy-duty conceptual engineering. As exciting as the idea of heavy-duty conceptual engineering sounds, it has never been developed or defended. In this paper, we pursue a two-fold goal. First, to offer a theory of heavy-duty conceptual engineering that distinguishes it from other kinds of conceptual engineering; second, to show that heavy-duty conceptual engineering is possible, both in theory and in practice, and to explain how it can be applied in the service of solving stubborn problems. The central idea is that heavy-duty conceptual engineering can enhance the semantic expressive power of a conceptual system by the use of bootstrapping processes. (shrink)