Author Reply: Grasping the Nebula: Inelegant Theories for Messy Phenomena

Often in science we are called upon to make grand pronouncements about our objects of study. What is the nature of this phenomenon to which we have become so attached, which we have labored over, and tended to in loving detail?

Standard practice is to put forth a grand unified theory, or GUT. A GUT hews to the scientific ideal of parsimony by describing a phenomenon in terms of necessary and sufficient conditions, often with a single rule. When a grand unified theory fails, it is assumed that we have simply articulated the wrong one. But what if our failure is not imperfect knowledge of our pet phenomenon, but a misapprehension that a good theory will be able to shoehorn everything into a fundamental law?

An impediment to would-be grand unified theories is that many natural phenomena—particularly those within the psychological sciences—do not have well-defined boundaries or a clear center of gravity. Call these psychological nebulae: rather than rigid, self-contained modules, they are an indistinct cluster of partially overlapping clouds, with foggy tendrils expanding into many domains. ¹ Nebulae are ill-suited to apprehension by grand unified theories. Such one-dimensional models leave off so much explanatory desiderata that they are doomed to be completely, comedically inadequate. ²

The fetishization of parsimony means that unwieldy theories are often dismissed on these grounds alone. But it is the theories which are unafraid of chaos that are best able to handle nebulae. ³ Messy theories should not only be tolerant of penumbral fuzz around the edges, but receptive to the possibility that the nebula contains no central, essential core. ⁴ No doubt there is something less satisfying about settling for inelegance, but the best theories won’t always feel right. Elegance is not a suitable heuristic for veracity. ⁵ Good theory-making retains all important details, no matter how awkwardly they cleave to the rest of the phenomenon. ⁶ This process is still capable, though, of judiciously slicing away the flimsiest proposals. ⁷ Good theories are just parsimonious enough.

Since nebulae crop up across multiple disciplines, they benefit from scholastic opportunism. Meaningful contributions can be made by conceptual analysis, informal observation, introspection, and phenomenological methods more generally. But it is crucial to separate what this sort of evidence can provide and what it cannot. The chief value of these perspectives is idea generation, and a check against the ever-narrowing focus encouraged by the grand unified theory tradition. ⁸ Phenomenology can resonate with us, it can lend a patina of understanding, but it is not equivalent to an empirical claim. ⁹ If our goal is to get at truth and not just truthiness, we must defer to data. ¹⁰

Under ideal circumstances, a theory carves nature at its joints. But this is only possible when nature is jointed. In selecting what type of theory to build, we should consider the properties of the phenomenon we are trying to grasp. Complex phenomena require more convoluted, nuanced explanations than have traditionally been marshaled for this task. Given their heterogeneity and unboundedness, it is possible that some nebulae can never be fully captured by any theory, no matter how inclusive. The goal of nebular theories may be less about definitive truths than postulating relationships between entangled systems and creating novel testable hypotheses. Their virtue lies not in their finality, but their ability to slouch us towards an incrementally better understanding of a sprawling, deeply intricate spectacle.