In philosophical discussions, we bring up the notion of plausibility a lot. “That’s implausible” is a common form of objection, while the converse “That’s plausible” is a common way of offering a sort of cautious sympathy with an argument or claim. But what exactly do we mean when we claim something is plausible or implausible, and what implications do such claims have? This question was, for me, most recently prompted by a recent pair of blog posts by Justin Weinberg over at Daily Nous on same-sex marriage. In the posts and discussion, Weinberg appears sympathetic to an interesting pedagogical principle: instructors may legitimately exclude, discount or dismiss from discussion positions they take to be implausible.* Further, opposition same-sex marriage is taken to be such an implausible position and thus excludable/discountable/dismissable from classroom debate. Is this a legitimate line of thought? I’m inclined against it, and will try to explain why in this post.**
What is plausibility?
Right off the bat, we should try to get clearer on the concept of plausibility. Unfortunately, there doesn’t seem to be a rich literature on this (Though I encourage commenters to enlighten me here!). Plausibility is admittedly a well-explored issue in epistemology, especially since a 1981 article by Dennis Packard, but the literature there seems to presuppose without discussion a background understanding of what plausibility is, and concerns itself with formal ranking models. More usefully, Nicholas Rescher (2005) has offered 3 different (plausible?) conditions for a claim’s being plausible: (1) When a preponderance of evidence favors it; (2) when it holds in more possible worlds than its negation; and (3) when credence in it passes some probability threshold, like 1/10. I don’t like definitions (1) and (2) as the notion of plausibility collapses into roughly what one is justified in believing, which is too narrow. (3) is more appealing, as it straightforwardly allows one to say one (weakly) believes X is correct but that ~X is plausible – which I take it is sometimes how the notion is deployed.
The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.