In current studies on the production of scientific knowledge, there is a predominant tendency to analyze the production of scientific knowledge through its relational structure, leaving analysis of the capacities of the scientists who influence the research processes in the background. In this paper, we argue in favor of a different direction. Specifically, we argue that scientists and their capacities –understood operationally– are an indispensable condition for the production of knowledge. In order to defend this position, we will first present two theories representative of this tendency and then show their limitations when it comes to analyzing the relationships and networks that make it possible to produce knowledge and to study the results of these relationships, but which are incapable of explaining the role played by scientists and their capacities within this. Secondly, given this situation, we propose an operational characterization of scientists and their capacities in the production of scientific knowledge. This characterization will be developed on the basis of Rheinberger’s theory of experimental systems. Based on this, we will propose our own interpretation of some of Rheinberger’s references to scientific capacities and their specific relationship with experimental systems. This interpretation highlights how non-thematic operations and knowledge affect the recognition of anomalies and enable concrete interventions in the experimental system, thus enabling the production of knowledge.