ABSTRACT
Philosophical and scientific requests for definitions often arise as “what is” questions. Here, noûs consists in proposing noteworthy features in virtue of which a thing or kind of thing, K, is to be identified. Proposals of that sort are apposite when users' ideas about what it is a K-designating term picks out are sketchy, muddled, conflicting, or contraindicated by available evidence. The primary goal is to enhance theoretical understanding of K; if possible, to discover what is so special about it. The method is to learn what makes it true that something is K or an instance of K. Such a definition might further support legislating what a term ought to mean to competent users. Consider the International Astronomical Union's 2006 redefinition of “planet,” informed by recent scientific research. Heretoforth, “planet” refers to a celestial body which, among other characteristics, has cleared the neighborhood around its orbit of other bodies (IAU 2007: 13–14). Certain items people believed or desired to be planets – notably, Pluto – now belong to a new category, “dwarf planet,” the members of which haven't cleared their neighborhoods. The IAU has fixed the extension of a pair of terms on the basis of what a planet evidently is, after all.
