This article discusses explanations behind theory choice, that is, ultimately, what leads people to accept a certain claim as valid. There has been a recent debate as to how closure was achieved in the continental-drift discussion. The controversy had found its usual explanation under rationalist terms: Wegener’s 1912 continental-drift theory was accepted 50 years later only after the plate tectonic theory had provided more evidence or a more in-depth problem-solving capacity. Nevertheless, a re-examination of the controversy under constructivist terms argued (...) that closure was achieved by a change in the style of thought. This analysis prompted some authors to react calling to a ‘defence of rationalism’ and insisting on explaining that the continental-drift theory was only accepted because of epistemic reasons. As the debate impacts on the way to explain scientific controversies, in this article I analyze rationalist and constructivist approaches with respect to ways to explain the social acceptance or rejection of a theory. The analytical perspectives will be contextualized within a broader theoretical discussion in philosophy and social sciences about the role of different factors that condition knowledge, which will also include an empirical approximation in the analysis of GMO and continental-drift controversies. Ultimately, the debate with rationalism is situated in a broader context about the ways of explaining the social acceptance of a theory, arguing that the problem with the rationalism that confuses a purely logical explanation with a sociological one is that it tends to judge rather than understand. (shrink)