Realists hold that science seeks to discover entities and process that exist in nature independently of whether these are accessible to our senses. This pursuit requires the development of new concepts as part of the research process, and thus requires learning new modes of thought, which is the basic source of incommensurability. I sketch a theory of conceptual content that explains how new concepts are introduced as modifications of existing concepts, and how the resulting continuities allow innovators to promote new ideas in a coherent manner. An account of evidence is proposed that explains how items under study constrain the choice of concepts, thereby limiting the scope of incommensurability and promoting pursuit of the realist goal.