Science of the gaps

We consider the problem of evaluating and expanding upon speculative hypotheses about the origin of life. The combination of life's complexity and its potential for historical contingency makes missing knowledge and missing ideas, which we term 'gaps', obstructive for an unusually wide variety of its most basic questions. The methods of scientific empiricism developed to justify beliefs in mature and stable sciences have proved less useful for reasoning through gaps, where criteria of consistency may rarely be met, and weaker criteria such as metaphor serve as motivations in practice. We consider the particular role of scenarios in the justification of speculative hypotheses, as they relate to questions of chance and necessity and the sources of causation. We demonstrate how making causal frameworks explicit may support more systematic reasoning about speculative and fragmentary hypotheses than the scenarios in which they are often framed.This article is part of the theme issue 'Origins of life: the possible and the actual'.