The hybrid constitution of psychiatry carries important implications for understanding the discipline and the legitimacy of its research approaches. One implication concerns the central role of concepts in forming the knowledge base of psychiatry. Because of this, it is vital to explore the structures and interrelationships of concepts through their historical constitution. Using this approach to compare concepts of empathy as articulated by R Vischer, T Lipps and E Stein shows that, despite overlap, the concepts vary in structure, in meaning and in the aspect of reality they capture. This suggests that the concept of empathy carries an unstable ontology and epistemology. In turn, this carries implications for the concept itself, for psychiatry and for research approaches in this field.