Semantics: a coursebook, second edition
tải về 1.74 Mb. Chế độ xem pdf
|
| Sense properties and stereotypes
99 of that predicate. For example, the ‘dictionary de finition’ which the speaker accepts for cat can be used to decide what is a cat, and what is not, thus de fining, implicitly, the set of all cats. Now we’ll consider the implications of this envisaged relationship more closely. We need to recognize the concepts of necessary and su fficient conditions. Definition A NECESSARY CONDITION on the sense of a predicate is a condition (or criterion) which a thing MUST meet in order to qualify as being correctly described by that predicate. A SUFFICIENT SET OF CONDITIONS on the sense of a predicate is a set of conditions (or criteria) which, if they are met by a thing, are enough in themselves to GUARANTEE that the predicate correctly describes that thing. Example Take the predicate square, as usually understood in geometry. ‘Four-sided’ is a necessary condition for this predicate, since for anything to be a square, it must be four-sided. ‘Plane figure, four-sided, equal-sided, and containing right angles’ is a su fficient set of conditions for the predicate square, since if anything meets all of these conditions, it is guaranteed to be a square. ‘Four-sided and containing right angles’ is not a su fficient set of conditions for square. Many non-square shapes, such as rectangles and trapezoids, meet these conditions. ‘Three-sided’ is not a necessary condition for square. Practice (1) Is ‘three-dimensional object’ a necessary condition for the predicate sphere? Yes / No (2) Is ‘three-dimensional object’ a necessary condition for the predicate circle? Yes / No (3) Is ‘three-dimensional object and circular in cross-section’ a su fficient set of conditions for sphere? Yes / No (4) Is ‘three-dimensional object and with all points on surface equidistant from a single point’ a su fficient set of conditions for sphere? Yes / No (5) Is ‘male’ a necessary condition for bachelor? Yes / No (6) Is ‘adult, male, human, and unmarried’ a su fficient set of conditions for bachelor? Yes / No Feedback (1) Yes (2) No (3) No (e.g. a cylinder) (4) Yes (5) Yes (6) Yes, for us, though some would debate the point, arguing, for example, that a monk or a Catholic priest meets these conditions but could not correctly be called a bachelor. For us, monks and priests are bachelors. PA RT T H R E E . . . to sense 100 Comment Obviously, we are stating conditions on predicates in terms of other predicates in the language. Henceforth, we will drop the quotation marks, and envisage necessary and su fficient conditions as relationships between predicates. Thus we shall say, for example, that animal and cat are semantically related in such a way that the applicability of the former is a necessary condition for the applicability of the latter. (Nothing can be a cat without being an animal.) In fact it is possible to give complete de finitions of some predicates in the form of a ‘necessary and su fficient list’ of other predicates. Kinship predicates and shape predicates are well-known examples. Practice (1) Is father adequately de fined as male parent? Yes / No (2) Is female spouse an adequate de finition of wife? Yes / No (3) Is parent’s father an adequate de finition of grandfather? Yes / No (4) Is hexagon adequately de fined as five-sided plane figure? tải về 1.74 Mb. Chia sẻ với bạn bè của bạn:
|