In Kameyama's account, only one zero-pronoun encodes the Cb, and any other zero-pronouns be­come Cfs, just as if they had been overtly ex­pressed in the sentence. In other words, when there are multiple zero-pronouns, only one of the zero-pronouns has any significance, and any other zero-pronoun might as well have been overtly expressed. But, because entities become zero-pronouns in or­der to avoid unnaturalness due to redundancy, zero-pronouns can be said to be salient enough to be un­derstood without being overt. In effect, this means that a greater amount of attention is placed on them than entities that were overtly expressed. This is shown through an example.

Taking her approach, some simple extensions are made to see how well the ordering of entities in cen­tering would work for multiple zero-pronouns. First, the antecedent for the Cb-encoding zero-pronoun is chosen-as shown in [Kameyania 85], Basically, this consists of choosing the entity with the highest de­gree of salience in the previous sentence. Then, the next most salient zero-pronoun according to the or­dering of degrees of salience given in the previous section is considered. The antecedent for this zero-pronoun is the most salient entity from the previ­ous sentence which will not contradict any possible constraints. At this point, we only consider seman­tic constraints for excluding such sentences as "The desk ate fish" and contra-index constraints for ex­cluding such sentences as "Jack ate Jack." Any other zero-pronouns are handled in the same manner. For example, the following discourse is examined:

Example 1:

(1) Taro wa Jiro to shokuji chuu de atta. Taro Top/Sub Jiro with meal during was Taro was having a meal with Jiro.

(2) $ Saburo wo mikaketa. Sub Saburo Obj saw (Taro) saw Saburo.

Cb: Taro, Cf: Saburo

(3) $ $ Jiro ni shoukaishita. Sub Obj Jiro Obj'2 introduced (Taro) introduced (Saburo) to Jiro.

(4) $ $ Shokuji ni sasotta. Sub Obj meal Obj2 invited (Taro) invited (Saburo) to the meal.

In sentence (1), the Cfs are ordered as Taro > Jiro, since Topic is the most salient entity. In sentence (2), the entity with the highest degree of salience from the previous sentence (Taro) is chosen as the zero-pronoun's antecedent, and becomes the Cb, with Saburo becoming a Cf. In the third sentence, after Taro is chosen as the subject of the sentence, since there is only Saburo left, Saburo becomes the an­tecedent of the object zero-pronoun, assuming that there is some sort of knowledge preventing Taro from becoming the object.

After sentence (3), the ordering of noun phrases would be as follows:

This means that sentence (4) is ambiguous, having the following possible interpretations:

(a) Taro invited Jiro to the meal.

(b) Taro invited Saburo to the meal.

But, the preferred meaning is (b). So, this would mean that the ordering should be as follows:

Taro > Saburo > Jiro

This example shows that when trying to interpret more than one zero-pronoun, the ordering of noun phrases according to Kameyama's account may not be optimal. Of course, this can be rectified by chang­ing the ordering of the degree of salience so that Ob­ject is higher than Object2, and as noted later in the paper this will actually take place. But, suppose sen­tence (3) in Example 2 is replaced with the following sentence:

(3') <3> <J> Jiro wo shoukaishita. Sub Obj2 Jiro Obj introduced (Taro) introduced Jiro (to Saburo).

Even in this case, the interpretation of sentence (4) would not change. So, the ordering of zero-pronoun not being optimal, i.e. that zero-pronouns are more likely to become zero-pronouns again than overt noun phrases, would seem to be the more log­ical choice.

So, we propose that "entities that have become zero-pronouns arc more centered in the discourse than those that have been overtly expressed." There­fore, the centering model has been extended to the following two lists to handle entities (noun phrases) that appear in a sentence:

In Japanese, both overt and elided pronominal forms exist. The elided pronominal form (zero-pronoun) was discussed in the previous subsection. In this subsection, we will show how pronouns are handled within the proposed model.

In Kameyama's account, pronouns do not encode Cbs and can only become Cfs. If overt pronouns arc treated as entities that were overtly expressed (i.e. put in the Possible Center List), the following example will not be interpreted correctly*.

Example 2; (1) Taro wa Jiro to hanashileita.

Taro Top/Sub Jiro with talking Taro was talking with .Uro.

CL: -, PCL: 'faro > Jiro (*2) <l> Ilanako wo mikaketa.

Sub Ilanako Obj saw (Taro) saw Ilanako.

OL: Taro, PCL: Hanako (Taro) likes (Ilanako).

If this example is interpreted with the antecedent of kanojo (her) in sentence (3) in the Possible Cen­ter List, then the interpretation would be 'Taro likes Jiro.' In order to obtain the preferred interpretation, the ordering of noun phrases should be as follows:

Taro > Ilanako > Jiro

This example shows that pronouns are not neces­sarily at the same level as with other overt noun phrases. In other words, pronouns are at a. level of attention higher than 'ordinary' noun phrases. This is especially true when considering the fact that pro­nouns are used to prevent unnaturalncss due to re­dundancy, just as zero-pronouns arc used.

3lCL' stands for Center List., and 'PCL' stands for Possible Center List.

So, we propose that pronouns be interpreted at the same level as zero-pronouns as follows:

Center List Model

The entities in a sentence belong to one of the following two lists:

(1) Center List ■•• Entities that have become zero-pronouns or overt pro­nouns.

(2) Possible Center List ■ ■ ■ Entities that were overtly expressed but are not in the Center List.

Entities in the Center List are more salient than those in the Possible Center List, with the exception of Topic.

The exception will be touched upon in the next sub­section.

Next comes the problem of ordering within the Center List and the Possible Center List. In other words, the difference in salience between pronouns (zero and overt) and 'ordinary' noun phrases is shown by the Center List and the Possible Center List. Entities in tin; Center last are more salient than those in the Possible Center List, lint, what about the difference in salience within each list?

In our model, the ordering is as follows:

Topic > Subject > Object > Object'2 > Others > Subject/Object/Ohjcct2 of subordinate clausi > Others in subordinate clause

The first line shows the ordering of grammatical functions of the main verb. This line is basically the same as Kameyama's ordering, except that Object is deemed to be more salient than Object2. This was because, after making some preliminary evaluations of our model, Object was found to bave a slightly higher degree of salience than Object,2.

The following two lines are for any entities that appear in subordinate clauses. There doesn't seem to be a clear cut difference between the Subject, Ob­ject, and Objecl/2 of subordinate clauses, so they are handled at the same level. The difference between the main clause and any subordinate clauses cap­tures the intuition that, entities in the main clause are more salient than those in subordinate ones.

There is one exception to the Center List Model. It is the salience of the Topic in the Possible Center

List. As can be surmised from the term itself, the Topic is special in that the sentence contains infor­mation about the entity corresponding to the Topic. In other words, the sentence is usually about the Topicalizcd entity. So, it was placed at the same level as the Object in the Center List.