This papers comments on the contributions of "ZDM Mathematics Education" dedicated to the theme "Perception, interpretation and decision making: understanding the missing link between competence and performance". The papers within this issue are brought together under the perspective of the stated aims of this issue, and then questions are raised about assumptions underlying methods of the studies and the overall enterprise. It becomes clear that teacher competence is a shining example of how in mathematics education both researchers and teachers need to develop a shared approach to negotiating meaning of terms used partly technically so that the use of the same terms for different things and different terms for essentially the same thing is reduced. The commentary aims to contribute to a joint understanding of the concepts used, so that researchers can communicate effectively with each other and so that their findings can support teacher development.