This paper takes up the concept of ‘crisis’ at both historical and historiographical levels. It proceeds through two examples of periods that have been described by historians of physics using a language of crisis. The first examines an incipient German theoretical-physics community around 1900 and the debates that concerned the so-called ‘failure’ of the mechanical world view. It is argued, largely on the basis of what is now an extensive body of secondary literature, that there is little evidence for a widespread crisis in this period. Abandoning the term as both description and explanation, one comes to the far more intriguing suggestion that the conflict over foundations was not evidence of a divisive dissonance but rather of collective construction. What has been termed crisis was, in fact, the practice of theoretical physics in the fin de siècle. The second example is the period either side of the advent of quantum mechanics around 1925. Different subgroups within the theoretical-physics community viewed the state of the field in dramatically different ways. Those, such as members of the Sommerfeld school in Munich, who saw the task of the physicist as lying in the solution of particular problems, neither saw a crisis nor acknowledged its resolution. On the other hand those, such as several researchers associated with Niels Bohr's institute in Copenhagen, who focused on the creation and adaptation of new principles, openly advocated a crisis even before decisive anomalies arose. They then sought to conceptualize the development of quantum mechanics in terms of crises and the revolutions that followed. Thomas Kuhn's language of crisis, revolution and anomaly, it is concluded, arises from his focus on only one set of theoretical physicists. A closer look at intra-communal differences opens a new vista onto what he termed ‘normal’ and ‘revolutionary’ science.

Theoretical astrophysics emerged as a significant research programme with the construction of a series of stellar models by A. S. Eddington. This paper examines the controversies surrounding those models as a way of understanding the development and justification of new theoretical technologies. In particular, it examines the challenges raised against Eddington by James Jeans, and explores how the two astronomers championed different visions of what it meant to do science. Jeans argued for a scientific method based on certainty and completeness, whereas Eddington called for a method that valued exploration and further investigation, even at the sake of secure foundations. The first generation of stellar models depended on the validity of Eddington's approach – the physics and many of the basic facts of stars were poorly understood and he justified his models through their utility for future research and their robustness under challenging use. What would become theoretical astrophysics depended heavily on this phenomenological outlook, which Jeans dismissed as not even science. This was a dispute about the practice of theory, and it would be this methodological debate (rather than the emergence of new facts or the incorporation of new theory) that made theoretical astrophysics viable.