Hyponymy

The lexical relation corresponding to the inclusion of one class in another is hyponymy. Defining hyponymy is less straightforward than defining cognitive synonymy. For reasons which will become apparent in due course, it is necessary to restrict the type of sentence used in the definition. Ideally one would like to be able to give a general characterisation of suitable sentence types; unfortunately this is not at present possible. What we shall do instead is to restrict the definition to one selected sentence type which happens to work, namely, that represented by the schema A is f(X), where f(X) is an indefinite expression, and represents the minimum syntactic elaboration of a lexical item X for it to function as a complement of the verb to be. X will be said to be a hyponym of Y (and, by the same token, Y a superordinate of X) if A is f(X) entails and is entailed by A is f(Y):

This is a DOG unilaterallyentails This is an ANIMAL.

That is a STALLION unilaterallyentails That is a HORSE.

This is a SCARLET flower unilaterallyentails This is a RED flower.

He is a man who MURDERED someone unilaterallyentails He is a man who KILLED someone.

Even with sentences not of the form A is f(X) it is often the case that a sentence containing a hyponym unilaterally entails a parallel sentence which is identical in all respects except that it contains a superordinate in place of the hyponym:

John punched Bill unilaterally entails John hit Bill.

She wore scarlet shoes unilaterally entails She wore red shoes.

Conversely, unilateral entailment between two sentences differing only in respect of the lexical fillers of a particular syntactic slot is often an indication of a hyponymous relation between the lexical units. However, the many and varied exceptions to both these general tendencies render it impracticable to frame a more general definition of hyponymy along these lines. In the following sentences, for instance, the entailment (unilateral in each case) is in the “wrong” direction (i. e. from superordinate to hyponym):

It’s not red entails It’s not scarlet.

All animals are forbidden entails All dogs are forbidden.

I always avoid the red ones entails I always avoid the scarlet ones.

Without the red ones there will still be too many entails Without the scarlet ones there will still be too many.

If it is red_, it will be rejected entails If it is scarlet, it will be rejected.

It is possible to formulate rules for predicting the direction of entailment in such cases. For instance, if the hyponym and superordinate fall within the scope of a negative, or a universal quantifier (e. g. all, every, each), or if they form part of a conditional clause or other expression of contingency, then the direction of entailment will be reversed. However, there are complications. For instance, the three factors mentioned interact with one another, so that if any two are simultaneously applicable, the entailment is in the ‘normal’ direction, i. e. from hyponym to superordinate. In 1, dogs and animals are within the scope (“field of action”) both of the negative not and the universal quantifier all; in 2, scarlet and red are within the scope of not, and form part of a conditional clause; in 3, cars and vehicles are within the scope of all, and are part of a conditional clause:

1) Not all dogs are dangerous entails Not all animals are dangerous.

2) If it is not scarlet, it will be rejected entails If it is not red it will be rejected.

3) If all cars are forbidden, I shan’t go entails If all vehicles are forbidden, I shan’t go.

When all three factors apply, entailment is once again reversed:

4) If not all vehicles are forbidden, I shall go entails If not all cars are forbidden, I shall go.

(Some readers may find this last example difficult to construe. Think of it this way: if it is the case that an incomplete embargo on vehicles will result in my going, then anything that entails an incomplete embargo on vehicles will result in my going; an incomplete embargo on cars entails an incomplete embargo on vehicles, so an incomplete embargo on cars will result in my going.) These regularities follow from elementary logical principles. However, while the logical principles are straightforward, the application to natural language is not quite so straightforward, because the crucial factors — negatives, conditionality, etc. — may not be overtly expressed.

5) It is important to avoid red socks entails It is important to avoid scarlet socks.

6) It is important to buy red socks does not entail It is important to buy scarlet socks.

7) Flowers are prohibited entails Dandelions are prohibited.

8) Flowers make an acceptable present does not entail Dandelions make an acceptable present.

There are no overt elements in these sentences to explain the differences; presumably, however, 5 and 7 contain implicit universal quantification.

These are not the only problems. In another class of instances, hyponym and superordinate in parallel positions yield no entailment at all. For example, It turned scarlet does not entail It turned red, since the referent of it may have been some other shade of red to begin with; nor, obviously, does the reverse entailment hold. For somewhat different reasons in each case, there is not entailment between I chose the first rose on the list and I chose the first flower on the list, nor between Mary was disappointed to receive a rose and Mary was disappointed to receive a flower (perhaps she was expecting an orchid?).

Entailment can occur between sentences differing only in respect of the lexical fillers of a particular syntactic, slot even when the lexical items in question are not related by hyponymy. This introduces further complications into the task of providing a principled account of the relations between hyponymy and entailment; 9 provides an example:

9) The boil is on John’s elbow entails The boil is on John’s arm.

It should be clear by now that the relations between hyponymy and entailment are quite complex; however, the definition of hyponymy adopted earlier bypasses these problems, so we shall pursue them no further.

There are other diagnostic tests for hyponymy which are either discriminatory but insufficiently general, or general but insufficiently discriminatory. For instance, a hyponym is often cognitively equivalent to a paraphrase in which a superordinate is syntagmatically modified. The equivalence between queen and female monarch, and kitten and young cat, for instance, establishes queen as a hyponym of monarch and kitten as a hyponym of cat. Where such equivalences can be found, they constituted satisfactory proof of hyponymy. However, by no means all hyponyms stand in a relation of cognitive equivalence with an expression containing a superordinate. There is, for example, no possible syntagmatic modification of animal which would reader it cognitively equivalent to dog (or elephant, mouse, crocodile...).

Hyponymously related lexical items occur normally, in the appropriate order, in expressions such as the following:

Dogs and other animals.

There’s no flower more beautiful than a rose.

He likes all fruit except bananas.

She reads books all day — mostly novels.

Any attempt to frame a definition along these lines, however, would run aground because, although such a definition could be made fairly general, it would not discriminate sharply enough to provide a guarantee of hyponymy.