Having a well-founded insight into the characteristics of teachers inquiry-based attitude (IA) supports operationalising IA as a learning goal in teacher education (TE). The aim of this study is to refine the notion of IA from an ill-defined global concept into something with reliable and valid characteristics. To do so, data were gathered on three different occasions amongst three different cohorts of teachers who participated in a master's programme at a Dutch university for applied sciences. This process of exploration and reconceptualisation was performed in collaboration with teacher educators. The results indicate that, statistically, IA has an internal reflective dimension and an external knowledge-sourcing dimension. Both dimensions can also statistically be differentiated from the personality traits openness to ideas, openness to change and epistemic curiosity. The implications of these findings for TE, plus recommendations for future research, are addressed.