The proposal of a shift in argument structure in the presence of a directional phrase means formally that each verb of manner of motion has two distinct entries in the lexicon. The verb walk, for example, will be assigned the representations shown in res29, with the corresponding surface projection of each argument structure. The verb in res29a is unergative, with a single argument in the external argument position. The verb in res29b is unaccusative, with an empty external argument position, an underlying direct object and a mandatory directional phrase (PATH).
John walked.
John walked to the store.
The lexical rule which creates the entry in res29b from res29a therefore demotes the argument which fulfills the role of actor in the event expressed by the verb from an external argument to an internal argument, leaving the external argument position open.
The shift in argument structure is proposed by to account for certain syntactic phenomena as discussed above, but it may have certain implications for semantic interpretation. The demotion of an external argument to an internal argument position is an operation which has unclear side-effects in terms of thematic structure and lexical semantics. That argument must maintain its thematic role, as the the actor remains an actor even when the sense of the manner of motion verb is extended to a directed motion use. This argument structure demotion is therefore problematic under the assumption of linking rules which map semantic arguments to syntactic argument positions: in these cases we have the same semantic argument being mapped to two different syntactic argument positions. There is no clear semantic difference in the function this argument serves in the two cases which could be a distinguishing factor in the application of the linking rules. There would therefore be ambiguity in the potential argument structures for many verbs as dictated by the linking rules. Levin and Rappoport Hovav avoid these issues by not discussing any aspect of the (lexical) semantic representation of the verbs they are attempting to account for syntactically.
The directed motion sense of manner of motion verbs can be triggered by either an explicit prepositional phrase res31 or by the discourse context, as we saw above in res30. Furthermore, we noted in the previous section that this directed motion sense does not necessarily entail a change of location to a particular point and is therefore not necessarily strictly resultative.
John walked to the store/around in circles/in place.
Because of these semantic properties, it seems rather unintuitive to assume that the underlying representation for a manner of motion verb may differ depending on whether a directional phrase is explicitly present or not. The directed manner of motion interpretation one gets of a manner of motion verb when it appears with a directional phrase is not a result of a sense shift in the meaning of the verb. Rather, it is a result of the composition of the meaning of the directional phrase with the meaning of the verb (cf. Dowty 1979; Moens and Steedman 1988; Jackendoff 1983, 1990; Pustejovsky pustejovsky:95a).
Motion verbs do not lexically encode a path, but they are also not incompatible with a path. In fact, it could be argued that due to their nature, motion verbs have a potential path argument. When these verbs appear with a directional prepositional phrase (PP), the PP extends the motion relation and thereby is interpreted as expressing the path which the motion follows. Directional phrases (such as to the store or towards the park in contrast with in place) which encode a path with an endpoint additionally indicate that the motion is following a path to a particular end location. Whether or not this end location is interpreted as the result location depends on the nature of the preposition heading the phrase. Thus all that is required to achieve the correct interpretation of the sentence is the integration of the meaning of the directional phrases with the verb semantics. Whether this meaning comes from context or from overt specification in the sentence is unimportant. The implication of these points is that manner of motion verbs on a directed motion use do not need to be collapsed with resultatives into a single treatment.
A lexical rule which extends the sense of manner of motion verbs in the presence of a directional phrase is unnecessary. The extended sense follows from the merging of lexical semantic properties of the verb with the meaning of the directional phrase. The criticism of the use of such a lexical rule is further strengthened by the observation that the context can trigger a sense shift of a verb, independent of the syntactic frame in which the verb appears. The lexical rule approach is thus semantically overrestrictive. The semantic evidence in the case of manner of motion verbs to a directed motion sense favors a non-lexical treatment of the sense extension.