Theory choice, the problem of accepting/rejecting scientific theories, is philosophically interesting in part because it involves appeal to nonempirical factors that can only be justified by philosophical considerations. The emphasis in this paper is on the historical as opposed to the experimental sciences—including astronomy, evolutionary biology, and especially historical geology—with examples taken from seventeenth through nineteenth centuries. The fact that evidential reasoning inherently requires a choice of philosophical/methodological principles is demonstrated through reference both to historical cases and to general philosophical considerations. This paper argues that methodological principles play a crucial role in turning empirical data into evidence for/against theories, and it outlines some of the particular evidential and methodological difficulties faced in the historical sciences. Choices of methodological principles depend on nonempirical factors, and because definitive arguments can rarely be found, they are largely a matter of judgment. “Scientific” debates are thus sometimes really disputes over philosophical taste and judgment. Moreover, it is often the case that clear judgments about the incorrectness/correctness of a methodological principle used in a specific context can only be made retrospectively. In part by looking at connections among Isaac Newton, David Hume, and Charles Lyell, and in part by examining Lyell’s own arguments, I argue that it was reasonable for Lyell to adopt uniformitarianism as a central methodological principle. Through arguments and historical examples, I also show that there are limits to the acceptability of the uniformitarian position.

Mainstream geology is founded upon uniformitarian concepts enunciated by James Hutton (1726–1797) and Charles Lyell (1797–1875), who argued that, during unlimited expanses of time, the Earth has undergone slow, ceaseless change by processes we can observe in operation. In their view, we cannot call on any powers that are not natural to the globe, admit of any action of which we do not know the principle, nor allege extraordinary events to explain a common appearance. A hypervelocity meteorite impact is an extraordinary event, originating from outside the Earth, and wreaking change instantaneously. Such a process violates every tenet of uniformitarianism. Largely for this reason, hypotheses of impact origin for craters on the Earth and the moon were vigorously opposed for the better part of the past century. Space-age research now has established beyond doubt the authenticity of impact as a geologic process, but an abundance of evidence exists that a wide chasm still persists between the views of impact specialists and those of terrestrial geologists. A full realization of the ramifications of impact processes may have been delayed by the advent of plate tectonics, which engulfed the geological community in the late 1960s. Revolutionary as it appeared at that time, plate tectonics, which is envisioned as involving gradual changes generated by forces internal to the globe, fully conforms with uniformitarian principles. In contrast, impact processes, which have recently been cited to account for cataclysmic events such as massive tsunami deposits, incinerating wildfires, and global extinctions, carry genuinely revolutionary implications that are fatal to the uniformitarian principle itself.