The starting point for the discussion of scientific discovery is Kuhn’s distinction between “normal science,” in which routine research is performed and the moments of crisis which can lead to paradigm shifts (Kuhn 1970, Chapters 3 and 4).Footnote 1 We begin with a description of scientific discovery within the context of normal science—that is, within the context of a given, accepted paradigm—before expanding to a consideration of an extra-paradigmatic dynamic. Working within a paradigm means, among other things, that there is an accepted “objective” set of methods, concepts, theories, and related expectations to which new experimental and theoretical results can be compared. While theoretical results tend to be more succinct, experimental results extend over a range of possibilities. To narrow the experimental field, I am specifically referring to the recorded reaction of a system either to an excitation (a signal) or to a specific set of conditions (a measured yield). In terms of ammonia synthesis within the framework of physical chemistry, if a specific amount of ammonia is sought, there is precisely one temperature at a given pressure that will provide this quantity from a given starting ratio of nitrogen and hydrogen. There is no strategy that will lead a scientist to another set of conditions that may be more beneficial to certain individuals for economic, political, or any other reason.

Among the activities of normal science, also called “fact-gathering” or “puzzle-solving,” Kuhn described three main pursuits. The first is the determination with increased accuracy of “that class of facts that the paradigm has shown to be particularly revealing of the nature of things.” These are measurable quantities, positions, characteristics, et cetera that are integral to the paradigm, for example, stellar position, electrical conductivity, chemical composition, or thermal properties. The second pursuit is the determination of “those facts that, though often without much intrinsic interest, can be compared directly with predictions from the paradigm theory.” Put simply, this pursuit is the demonstration of agreement between theory and experiment. It was a decisive factor in the interaction between Fritz Haber and Walther Nernst. The third activity “consists of empirical work undertaken to articulate the paradigm theory, resolving some of its residual ambiguities and permitting the solution of problems to which it had previously only drawn attention.” This activity, Kuhn argued, is the most important class of fact-gathering and can be broken down into three subcategories: the determination of physical constants, the determination of quantitative laws, and the application of the paradigm to other areas of interest. These activities are nearly the same for theoretical and experimental endeavors, especially paradigm articulation, though the amount of work devoted to each of the three classes of fact-gathering may differ.

To underscore that there is precisely one state of a physical system under defined circumstances, consider Kuhn’s attitude toward a particular form of paradigm articulation.

Few of these elaborate endeavors [to determine the value of universal physical constants] would have been conceived and none would have been carried out without a paradigm theory to define the problem and to guarantee the existence of a stable solution [italics added].

Returning to physical chemistry and the conditions for chemical synthesis, the accuracy to which we know the universal constants determines how well we can predict the outcome under our chosen state variables (see the constant R in the ideal gas law, for example). With these guidelines for identifying “normal” scientific activity, the case study of ammonia appears particularly appropriate. It is not only a clear-cut example of a scientific breakthrough, but it fulfills the criteria of normal science: the determination of physical constants (from thermal data), the comparison of experiment and theory, the resolution of ambiguities, and the formulation of quantitative laws.

Considering these elements of Kuhn’s theory, we may pose an interesting question. The breakthrough of ammonia synthesis is just that: a breakthrough and not a paradigm shift in any Kuhnian sense. It is a rare moment that results in the identification of especially pertinent and applicable scientific knowledge, not only for subsequent scientific undertakings but also for technological and industrial progress with potential for societal and/or cultural impact. But there is no mechanism in Kuhn’s description of “normal science,” apart from the arrival of a period of crisis leading to a paradigm change, that leads to anything but eternal fact gathering. Yet breakthroughs do exist—we have proof. What is it, then, that differentiates a mundane laboratory assessment from a historical, world changing experimental result? Why will one publication, based on years of meticulous research, receive no attention, be cited zero times, and descend to the depths of the sea of scientific literature while another becomes the basis for an industrial process that can help feed a third of the human population currently alive, provide vast munitions for the war machine, all while making meaningful contributions to the completion of a physical theory?

As I have hoped to illustrate in Parts I and II, it is a question of knowledge, talent, and intuition, but perhaps most of all, of circumstances.

We now turn to the Haze to reformulate the relationship between normal science and paradigm shifts.