I’ve been working through Plantinga’s latest volume, and was struck by a feature of his discussion of defeaters. For Plantinga, by definition a defeater prevents one from having knowledge. That means that one and the same belief can be a defeater for one person and not a defeater for another, since one of the two might have additional information that prevents the belief in question from counting against knowledge. Hence, being a defeater is not really a two-place relation between one belief and another, but rather (at least) a three-place relation between a certain belief (or experience), the belief being evaluated, and a noetic structure.
Even if unproblematic, about which I am still thinking, this result is surprising. I can’t see any good reason to develop a view of defeat in this way rather than the more common way.