At CERME13, the TWG17 worked to navigate ways forward amidst a diversity of theories in mathematics education research (MER). The TWG17 made explicit efforts to negotiate shared meaning for terms being used, emphasizing those that did not translate well from (or into) English. Interrogating the question of the scientificity of MER led to reflection on the value-ladenness of MER. Theoretical approaches (e.g., networking, adapting), rather than individual theories, organized discussion. Implications included continued attention to ontological, epistemological, axiological, and ethical dimensions of theorising, to explain affordances of theoretical and methodical choices.