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In view of the distribution of tone in the above phonological structures, we must confront the question of whether or not onset boundaries may remain completely toneless. In other words, given the present state of the model, it is logically possible to predict the generation of the following structure:

Chapter 6. Empty domains in phonological structure_______________________ 166 (23)*

N u

O N i O N 2 N Ll

[ X X [ X X X x ]

[ x ]

[ x ] [ x

There are many inter mediate levels

However, the interpretation of this structure — a contour characterised by continuous low pitch with dips — is unusual. Hence, we would wish the grammar to disallow the generation of such contours. Besides, the effect that empty nuclei have on following constituents which show toneless boundaries, although intuitively predictable — to pull down their interpretation in the frequency range — is, nevertheless, rather bizarre. The reason for this claim is that, if a unit is already interpreted as low pitch, no matter what factor may force it to be interpreted yet lower in frequency, there is no available space in the lower frequency range for it to be interpreted. Given this observation, it follows that, ideally, structures like this one should not be generated by the model.

When models à la Pierrehumbert encounter the latter situation — in their terms, a bitonal pitch accent can potentially trigger downstep on a following L — they stipulate that L tones do not undergo downstep, and thus, they safely use these structures to account for other pitch contours. Although this solution may be valid, note that it is based on a stipulation, and that the offending structure can still be generated in their models. In contrast, as far as the present model is concerned, I argue that the structure in (23) is rejected by imposing further constraints in the distribution of empty nuclei. Let us now examine which, these a r e .

In chapter 4 ,1 claimed that boundaries of prosodic domains participate in licensing relations, and that their licensing capacity controlled the distribution of tones. In this

Chapter 6. Empty domains in phonological structure_______________________ chapter the same principles apply, but additionally, they constitute another constraint on the occurrence of empty nuclei. This constraint is understood as follows: toneless boundaries of empty nuclei must license, or be licensed by, another boundary which bears tone. Let us formulate this constraint in terms of another licensing principle:

(24) Empty nuclei and boundary licensing

One of the boundaries of empty nuclei must participate in a licensing relation with another boundary which itself licenses T.

Given this condition, the structure in (23) above is rejected, since all the boundaries of empty nuclei violate this condition. Nevertheless, the well-formed structures which can be generated by the model are as follows:

(25) (a) both nuclear boundaries participate in a licensing relation in which other boundaries license T.

O N N

Chapter 6. Empty domains in phonological structure 168 (b) the nuclear right boundary participates in a licensing relation in which its

licensor bears T.

O N

I } I ^

[-] [x] [.]

(c) the nuclear left boundary participates in a licensing relation in which its licensor bears

O N N

m ,

['] [x] [•]

The solution I have adopted here not only excludes structures such as (23) from the model, but also allows us to impose more restrictions on the occurrence of empty nuclei.

The topic related to licensing relations between boundaries of empty nuclei and other constituents, leads us back to examine the occurrence of empty nuclei in initial position, in order to analyse what constitutes well-formed structures. In §2.1 I have stated that an empty nucleus may occur to the left of a nucleus whose left boundary is associated to T. In this position, this structure is sanctioned by empty-nuclei-and- boundary licensing. By the same token, notice that the following ill-formed structure results:

‘*In § 7 .1 1 shall treat this structure as ill-formed, since the presence or the absence o f [ ] yields two phonological structures which show the same phonetic interpretation, and therefore, are redundant.

Chapter 6. Empty domains in phonological structure_______________________ 169

(26)*

N 12

N L l

r It’s a [X] [ b y s m a l ]

As the arrows indicate, the right boundary of [bysmal] licenses the left boundary of [ ]. However, this structure is ill-formed because neither boundary of the empty nucleus performs the task of participating in a licensing relation with another boundary which itself licenses T. For this reason, I conclude that an empty nucleus is banned from appearing in this position, and thus, (26) results in being ill-formed.

This situation has a direct bearing on the question of how to account for contours such as the following:

(27)

Ifs a bysmal

that is, a rising movement preceded by relatively mid pitch. The structure I propose for this type of contour is as follows:

(27’) N L2

I

Chapter 6. Empty domains in phonological structure_______________________ 170 The only possible way to capture a rising movement over the last domain at Ll in this model is by the association of T to L2's right boundary. In addition, observe that Li's toneless left boundary already accounts for the drop in pitch. In other words, the step manifested in the FO contour is predicted by the presence of precisely this toneless boundary.

However, it may be argued that there are other pitch contours in which the starting point of the rising movement is higher thanlthe one illustrated above, and thus, that there is no manifestation of a step down in its phonetic interpretation. For instance, consider the following contour:

(28)

Ifs a bysmal

In view of this contour, the validity of the above representation in accounting for contours such as this is questioned.

A possible account of the difference between these contours in phonological representation might be that, in the former structure, an empty nucleus is the factor which pulls down the interpretation of the nucleus to its right (this is the structure in (26) above), whereas, in the latter structure, empty nuclei are absent, and consequently, this effect is absent, too. However, recall that this structure has already been rejected above by the principle of empty-nuclei-and-boundary licensing. Given this situation, the present state of the model forces us to treat those particular contours as allotonic interpretations of the same phonological structure^^.

follow Gussenhoven (1983) on the representation of rising movements in nuclear position. However, for ex a n çle Ladd (1983) maintains that the above contoms are in contrast. If this statement proves to be true, the present state o f the model may have to b e revised with respect to this particular point.

Chapter 6. Empty domains in phonological structure_______________________ Hj. I conclude the present discussion of this type of stepping contour by claiming that the proposed account has an advantage over that of Grice'95 and P'80^® in as much as it shows a principled way of accounting for tonal harmony by means of inter-onset licensing. In addition, it shows an improvement on that of P'80, in the sense that the phonological identity of pitch patterns at each new level remains unaltered with respect to identical patterns found in a non-stepping structure^^. Also, it avoids the tendency present in both Grice'92 and Ladd (1990) to elaborate toual structure in order to be able to capture the downstep phenomenon. On the other hand, this is achieved in the present model, by having recourse to the idea of empty nuclei, while maintaining the simplest tonal structure. Rnally, in the event of overgeneration, this model has recourse to general principles which exclude offending structures from being generated by its grammar. However, Pierrehumbert and her followers resort to a stipulation for the same purposes.