I assume that most of the ‘ content words’ in a language can be characterized in the lexicon in terms of their use as predicates. I take this to be true of nouns, verbs, adjectives,¹ most adverbs, and also a great many conjunctions. Thus a sentence like (24):

(24)Harry lives at home because he loves his mother

is evaluated as true or false depending not only on the joint truth-values of the two clauses which flank because, but on the truth or falsity of the ‘causal’ connection between the two situations named by these clauses. The sentence can be interpreted as having because as its main predicate, a predicate which takes two clauses as its arguments and which is used to assert a ‘causal’ or ‘logical’ connection between them.

As predicates, words can be described first of all according to the number of ‘arguments’ that they take. Thus the verbs ascend and lift are both motion verbs, they are both used to describe motion upward, but they differ in that while ascend is used only of the object that moves upward, lift requires conceptually two objects, one the object that is moving upward, the other the object or being that is causing it to move upward. Another way of stating this is: ascend is a one-argument predicate, lift is a two-argument predicate.²

Many verbs are flexible in the number of arguments they take. This is true, for example, of some motion verbs, like move and rotate, and many change-of-state verbs, like open and break. Move, as can be seen in sentences (25) -(27), can occur with one, two, or three arguments:

(25) The rock moved.

(26) The wind moved the rock.

(27) I moved the rock (with a stick).

Mention of the object which moves is required of all three uses; the two-argument uses additionally identify either the physical force or object which is directly responsible, or the animate being which is indirectly responsible, for the activity of moving; and the three-argument use identified all three of these (as in (27) with the parenthesized phrase included). The surface-contact verbs hit, touch, strike, etc., require conceptually at least two arguments in all of their uses, namely the objects which come into contact, but they accept as a third argument the animate being that is responsible for the coming-into-contact.

The verbs rob and steal conceptually require three arguments, namely those identifiable as the culprit, the loser, and the loot. The words buy and sell are each four-argument predicates, the arguments representing the one who receives the goods or services, the one who provides the goods and services, the goods and services themselves, and the sum of money that changes hands.

I have referred in to the conceptually required number of arguments. I am distinguishing this from the number of arguments that must be explicitly identified in English sentences. The various ways in which English grammar provides for the omission or suppression of conceptually required arguments. To say that conceptually rob or buy are three- or four-argument predicates respectively is to acknowledge that even when we say merely (28):

(28) She robbed the bank

we understand that she took something out of the bank, and when we say (29):

(29) She bought it

truthfully, it is necessarily the case that there was somebody who sold it to her and that a sum of money was exchanged.

¹ In other words, I accept the part-of-speech identities argued by George Lakoff in Appendix A of On the nature of syntactic irregularity (1965), Report no. NSF-16, Computation Laboratory of Harvard University; as well as the extension of such identities to ‘nouns’ proposed by Emmon Bach in ‘Nouns and noun phrases’ (1968), in E. Bach and R. Harms (eds.), Universals in Linguistic Theory, Holt, Rinehart and Winston.

² Of course, as motion verbs each of them may take time and space complements as well, as is seen in The balloons ascended to the rafters just after the speech ended. Since in general the nature of the time and space complements, we may permit ourselves to ignore such matters while discussing the typing of predicates on the basis of the number of arguments they accept.