1.2.3 Morphological criteria for determining category

What we have been looking at in the above paragraph is the morphological properties of words: the various forms we find for different words. Often morphemes constitute different pieces of words: the form ideas can be broken down into ‘idea’ and ‘s’, where the second piece represents the plural aspect of the word and is called the plural morpheme. The point is that only words of certain categories can host morphemes of certain types. Consider warms from (11). This, too, breaks down into two pieces, ‘warm’ and ‘s’. But the ‘s’ here is not the plural morpheme but another one which expresses something entirely different. This is the morpheme we get on words like hits, sees, kisses and imagines and it represents present tense, which has a number of meanings in English ranging from the description of what is taking place at the present moment to something that habitually happens:

1.2.3 Morphological criteria for determining category

Note that this morpheme cannot go in any of the words in (8) (except for weather, a fact that we will return to): ideas is not the present tense form of the word idea. Essentially then, different categories of words have different morphological properties and therefore one can distinguish between categories in terms of what morphemes they take: if it has a plural form, it is a noun and if it has a present tense form it is a verb.

1.2.3 Morphological criteria for determining category

What about cases like weather, where the form weathers can either be taken to be a plural form or a present tense form, as demonstrated by the following:

1.2.3 Morphological criteria for determining category

This is not an unusual situation and neither is it particularly problematic. Clearly, the word weather can function as either a noun or a verb. As a noun it can take the plural morpheme and as a verb it can take the present tense morpheme. There may be issues here to do with how we handle this situation: are there two entries in the lexicon for these cases, one for the noun weather and one for the verb, or is there one entry which can be categorised as either a noun or a verb? Again, however, we will not concern ourselves with these issues as they have little bearing on syntactic issues.

1.2.4 Distribution

The morphological forms hates and smiles are both present tense, indicating that the words are of the same category, i.e. verbs. However, as demonstrated by (20), these words appear to have different distributions and thus they belong to different categories. How can this apparent contradiction be reconciled? We will see that part of the solution to this problem follows from the way in which distributions are defined, which we have yet to discuss. However, another aspect of distribution can be discussed at this point. Note that a sentence in which the verb smiles would be grammatical, would be ungrammatical with the word hates:

1.3.4.1 Verbs

We have already seen that verbs take morphemes which express tense:

1.3.4.1 Verbs

The different forms of a word are known as its inflections and we say that verbs inflect for tense in that different forms represent tense distinctions. As discussed earlier, not all inflectional forms are regular and, especially in the past tense, we have irregular forms:

1.3.4.1 Verbs

We are not so much concerned with morphological or phonetic form in this book, so we can think of these past tense verbs as abstractly being a stem, i.e. the lexical verb, plus a past tense morpheme which we will represent as ‑ed though obviously this is not supposed to indicate a pronunciation:

1.3.4.1 Verbs

Virtually all verbs have a past tense form, with only a handful of very exceptional cases, such as lightening used as a verb, which can only appear in this ing form:

1.3.4.1 Verbs

The present tense inflection is slightly different to the past tense one. Compare the examples in the following:

1.3.4.1 Verbs

In (54) the verb has the same past tense inflection in all permutations of the sentence, but in (55) there is a difference between the first example and all the others. This corresponds to the fact that the argument which precedes the verb in the first case is third person and singular and in all other cases this argument is either plural or first or second person (I or you). This argument is called the subject and we will discuss its nature and properties in the next chapter. For now we will simply use the term to refer to the argument in front of the verb without further discussion. The morphological phenomenon shown in (55) is known as agreement. We say that the verb agrees with certain features (number and person) of the subject (later on, we will see that it is the inflection that agrees with the subject and that this is independent of the verb). English does not demonstrate much in the way of agreement inflection. For the vast majority of verbs it is only in the present tense and with a third person singular argument that the verb has an agreement form. The exception is the verb to be, for which there are three present tense forms (first person singular, third person singular and the rest) and two past tense forms (first and third person singular and the rest):

1.3.4.1 Verbs

The English verb has other inflectional forms expressing things other than tense. For example there are perfect and progressive aspectual forms:

1.3.4.1 Verbs

While tense typically places an event in time, aspect refers to the process of the event itself: whether it has stopped or is still going on, for example. Perfect aspect often denotes that an event has finished while progressive denotes that it is still continuing:

1.3.4.1 Verbs

To summarise, there are five forms in which an English verb can appear: the base form (uninflected), the past tense form, the third person singular present form, the perfective (and passive) form and the progressive fo

1.3.4.3 Adjectives

In many ways, then, this is like the missing plural *sheeps or the missing past tense *putted (as past tense of put, not putt, which is putted). As such fast is just an irregular adverb. In general, colour adjectives do not tend to form adverbs and the fact that this is a semantically well-defined class of adjectives indicates that there might be semantic reasons for it. This is further supported by the fact that colour adjectives that do form ‑ly adverbs, such as blackly, do so only if they have meanings that go beyond reference to the colour: blackly means ‘in a sinister or evil way’ and greenly can mean either innocently or enviously. Admittedly, the absence of size adverbs like *bigly and *smally is problematic given the existence of hugely and minutely. But putting this small number of problematic cases to one side, we can see that the ‑ly morpheme is a very productive one, applying to most adjectives. As pointed out above, most derivational morphemes, being lexical in nature, are not productive and apply only to selected lexical items.

1.3.4.3 Adjectives

The subcategorisation of adverbs is a rather more tricky issue. One would have thought that if adverbs are formal variants of the relevant adjective, then they would subcategorise in the same way as these adjectives – like the present tense verb subcategorises in the same way as the past tense verb. There are some cases where this might well be true:

1.3.5.1 Inflections

These two clauses express the same thematic content: a seeing relationship holding between Sam and me. However, they differ in a number of ways. In (135a) the verb is inflected for tense (past in this case) whereas in (135b) the verb is uninflected and cannot display tense distinctions:

1.3.5.1 Inflections

We call sentences with verbs inflected for tense finite clauses and those without, non-finite clauses. In finite clauses, the nominal element that is in front of the verb, if it is expressed as a pronoun, has a certain form, but it has another form in non-finite clauses:

1.3.5.1 Inflections

One argument in support of this treatment of finite inflections concerns the difference between inflectional morphemes and derivational morphemes, discussed above. A derivational morpheme forms a new word from an existent one in the lexicon. This new word has lexical properties of its own and may even differ in its meaning from the original word. Furthermore, the process tends to be limited, applying to a selection of lexical elements rather than to whole classes. Inflectional morphology, on the other hand, does not change the lexical element, it just provides another form of that word. Often, it adds some element of meaning (such as tense or plural) to the meaning of the original word rather than changing the meaning to something else. This all suggests that the two processes are very different and that derivational morphology is something that goes on in the lexicon to expand the number of available words. Inflectional morphology is, on the other hand, too regular to be a lexical process, applying to whole categories. This would seem to be the hallmark of a syntactic process not a lexical one. We will assume therefore that verbal morphemes expressing tense and agreement are independent words inserted into a sentence in their own position and undergo a subsequent syntactic process which combines them with the verb that they are attached to.

1.3.5.1 Inflections

One argument in support of this treatment of finite inflections concerns the difference between inflectional morphemes and derivational morphemes, discussed above. A derivational morpheme forms a new word from an existent one in the lexicon. This new word has lexical properties of its own and may even differ in its meaning from the original word. Furthermore, the process tends to be limited, applying to a selection of lexical elements rather than to whole classes. Inflectional morphology, on the other hand, does not change the lexical element, it just provides another form of that word. Often, it adds some element of meaning (such as tense or plural) to the meaning of the original word rather than changing the meaning to something else. This all suggests that the two processes are very different and that derivational morphology is something that goes on in the lexicon to expand the number of available words. Inflectional morphology is, on the other hand, too regular to be a lexical process, applying to whole categories. This would seem to be the hallmark of a syntactic process not a lexical one. We will assume therefore that verbal morphemes expressing tense and agreement are independent words inserted into a sentence in their own position and undergo a subsequent syntactic process which combines them with the verb that they are attached to.

1.3.5.4 Complementisers

We saw above how inflectional elements determine the finiteness of the clause, with modal auxiliaries and tense appearing in finite clauses and the non-finite to appearing in non-finite clauses. Complementisers are also sensitive to finiteness. That and if always introduce finite clauses, while for always introduces non-finite clauses:

1.3.6 Functionally underspecified categories

This would suggest that they are not categorised in the same way as inflections. They appear to be verbal elements as they inflect for almost the same set of things that verbs do (perfective have inflects for tense (has/had), progressive be inflects for tense (is/was) and perfect aspect (been) and passive be inflects for tense (is/was), perfect aspect (been) and progressive aspect (being)). However, they are clearly not thematic elements in that they play no role in the thematic interpretation of the sentence. Aspectual auxiliaries therefore share properties with verbs and inflections, but they cannot be categorised as either. We can capture this situation if, like verbs and inflections, we categorise aspectuals as [–N, +V] elements, but simply leave the [±F] feature undefined. In common with inflections, aspectual auxiliaries also take only verbal complements and they never precede any other category. However, they may precede either verbs or other aspectual auxiliaries:

2.2.1 The subject

When the subject refers to either the speaker or the addressee, what we call first and second person, the finite verb in present tense shows no overt morphology. The same is true when the subject is plural. However, when the subject is third person (referring neither to the speaker nor the addressee) and singular the present tense verb inflects with an ‘s’. This morpheme not only shows the tense therefore, but also the nature of the subject: that it is third person singular. This phenomenon is known as agreement: we say that the verb agrees with the subject.

2.2.1 The subject

Clearly English does not have much in the way of agreement morphology, usually distinguishing just the two cases given above, though the verb be has three agreement forms in the present tense and two in the past tense:

3.2.2.2 S-structure and Case Theory

In (84a) the clause is finite as tense is marked on the auxiliary verb. The subject he is in the nominative form, not the accusative him. However, the object of the verb help, her, is in the accusative not the nominative she. In (84b), while the main clause is finite and has a nominative subject, I, the embedded clause is non-finite. This clause has an accusative subject him. The object of the preposition in this clause is also accusative, us.

Chapter5 Verb Phrases

In this chapter we are going to take a detailed look at the structure of the phrase that is in some ways the core of the clause. In this phrase the basic argument structure of the clause is formed which is made up of the verb, acting as the predicate, its arguments and adjoined modifiers. Thus, it is within the VP that Θ-role assignment takes place. We will also see that it is within the VP that other aspects of semantic interpretation are represented, such as event structure and aspect. Other aspects of clausal interpretation, such as tense, modality and force are introduced in structures built on top of the VP and we will deal with these in the following chapters.

5.1 Event Structure and Aspect

Turning now to aspect. Again this is a semantic property of verbs which has to do with the process involved and its relationship to the progression of time. This is not tense, however, which situates an event at a particular place in time with respect to some other point, the time at which a sentence is uttered, for example. With aspect time is important with respect to the internal aspects of the event itself. For example, the end point of the event seen with respect to its starting point and what goes on between the two. It is important to distinguish between two types of aspect, one which is internal to the meaning of the verb, which we might refer to as lexical aspect, and one which is to do with the interpretation of a particular event described by a sentence, which we call grammatical aspect. Lexical aspect is also sometimes called aktionsart.

5.2.3.2 Light verbs and ergatives

Putting aside the issue of tense and agreement inflections, it is possible to give a very similar analysis of the Hungarian causative verbs to the one we proposed for English causatives, with a causative light verb introducing the causative interpretation and the agent subject:

5.2.3.2 Light verbs and ergatives

Thus the main verb stem moves to the causative light verb morpheme in order to bind it. The product of the movement would obviously have to undergo further morphological processes in order to show the appropriate tense and agreement forms, but this is unimportant for the point being made here. Suppose English works in exactly the same way as this. The English causative light verb is a bound morpheme, though a phonologically null one, and differs only in this way from the non-null causative make. Thus it must be attached to the main verb and this happens by the main verb moving to adjoin to it. This would then give us an independent motivation for the movement of the verb.

5.2.4 Transitive verbs

In (72a) we have the past tense form of the verb to saw, Sam is an agent and the wood is patient. In this cases a resultative modifier like to pieces can be used to describe the state of the object after being acted upon. In (72b) we have the past tense form of the verb to see, Sam is an experiencer and the wood is an unaffected theme. Obviously in these cases the resultative is inappropriate because nothing directly happens to the object as a result of being seen. We will put the case of the experiencer–theme type transitives to one side for the moment and start our discussion with the agent–patient type.

5.3.1 The auxiliary as a dummy

In these examples, the auxiliary do adds very little to the meaning of the sentence, apart from the fact that it carries tense. However, given that main verbs can do this, this is clearly not the main function of the auxiliary in these examples. Instead the auxiliary is used to do something that main verbs cannot do. In (158a), the auxiliary is moved to the front of the clause to form a question, in (158b) it is used to bear the contracted negative, in (158c) it bears stress in order to assert something that had previously been denied and in (158d) it is used to form a tag question, the main function of which is to lessen the force of a statement. As the following show, these are all things that we cannot use a main verb to do:

5.3.1 The auxiliary as a dummy

The ungrammaticality of most of the sentences in (159) shows that the main verb cannot be used in this way. That (159c) is not ungrammatical does not indicate that it is an exception, however, as this has a different meaning to (158c). In (159c), the emphasised verb is used to question or contradict a previous statement in terms of the content of the verb itself. So, for example, if someone claimed to have seen something that was invisible to others, (159c) might be an appropriate response. Importantly, (159c) could not be used to contradict someone’s claim that they did not see something, i.e. contradicting the truth of their statement. The point is, then, that the auxiliary do is inserted into a sentence to do something that is impossible for a main verb to do and hence it has a purely syntactic role rather than a semantic one. For this reason it is often called the dummy auxiliary. Perhaps its main function is to support the tense morpheme when, for whatever reason, this cannot appear on the main verb and hence the phenomenon is also called do-support.

5.3.1 The auxiliary as a dummy

Considering the semantic relationships that exist in these sentences, we notice that they are established between the subject and the predicative element after the verb: Tim and tall, Ferdinand and a fake and Gertrude and in the garden. Again, the main function of the verb here appears to be to support the tense morpheme and it seems to make very little contribution of its own. Indeed, in circumstances where there is no need to express the tense morpheme, the verb is not used:

5.3.1 The auxiliary as a dummy

The bracketed part of the sentences on the left in (161) express the same predication relationships as those on the right and the only difference between the two is the expression of tense in the latter. Thus it looks as though the copula is used to support the tense morpheme when predication relationships are established between a subject and a non-verbal element. It is interesting that the verb be is used in this case, not the verb do as it is in cases of do-support. Even though both elements seem to contribute little to the interpretation of the sentence, it seems that their use is specialised to certain contexts: do for cases where the main verb fails to be able to support tense and be for cases where there is no verb present to support tense. I know of no explanation for this fact.

5.3.1 The auxiliary as a dummy

What is the function of the auxiliary in these sentences? Note that the auxiliary bears some morpheme: in (162a) the tense, in (162b) the ing associated with the progressive auxiliary and in (162c) the tense on the first passive auxiliary and the en associated with the perfective have on the second. In these examples, the main verb cannot bear these morphemes for the simple reason that it is already bearing the passive morpheme and it seems a basic principle of English morphology that no word can bear more than one overt inflectional morpheme:

5.3.1 The auxiliary as a dummy

In these cases, there is an ambiguity that must be checked for. For example, what was seen in (164a) could either be taken to be an object (the treaty that was signed) or an event (the treaty being signed). It is the latter interpretation that is relevant here as this clearly involves a predication-like structure that simply lacks tense, similar to the examples in (161). Of course, the important observation is that here we have a passive construction involving a passive morpheme, but no passive auxiliary. This indicates that the function of the passive auxiliary is to bear an inflection rather than to add any semantic content.

5.3.2 The nature of the aspectual morpheme

Finally, presuming the clause to be finite, some element will have to bear the tense morpheme. As the verb cannot do this, the relevant dummy auxiliary will be inserted into the tense position: have in the presence of en and be in the presence of ing. In (167c) there is the extra complication that there are two aspectual morphemes as well as the tense morpheme. In this case the verb moves to the lowest aspectual morpheme, ing, and an inserted auxiliary will bear the other morphemes, be for the perfective and have for the tense:

5.3.2 The nature of the aspectual morpheme

With these assumptions then we can successfully account for the distribution of the aspectual elements in the English clause. We will provide more detail of the upper part of the clause structure including the tense and clausal subject position in the next chapter.

Chapter6 Inflectional Phrases

In chapter 1 we introduced the category of inflection, consisting of modal auxiliaries, the marker of the infinitival clause to and tense morphemes. It is with this category that we will be concerned in the present chapter. We will show that providing a standard X-bar treatment of this element solves a number of problems that we have noted in previous chapters.

6.1 The structure of IP

However, the traditional assumption is challenged by the analysis in (4), where it is claimed that clauses most definitely do have heads. There is much evidence to support this. Firstly consider the relationship between the inflection and the clause. The inflections come in two basic types: finite and non-finite. The finite inflections consist of the modal auxiliaries and tense morphemes. The infinitival marker to is non-finite, but we also get clauses, traditionally called participles, in which the inflection on the highest verbal element is either ing or en (or one of its irregular versions):

6.1 The structure of IP

The form of the inflection in (14) depends on properties of the subject. This phenomenon is known as agreement (see chapter 1). In English, agreement is very restricted, visible only in the case of the present tense morpheme and the present and past tense forms of be. We saw in chapter 4 that the possessive determiner also shows a similar pattern, having one form for pronominal possessors and another for non-pronominal possessors:

6.2.1 Inserting auxiliaries into I

In the previous chapter, we introduced the idea that dummy auxiliaries are inserted into a structure when the verb is unable to support a bound morpheme. Consider what happens with regard to a bound inflectional element such as the present tense morpheme s:

6.2.1 Inserting auxiliaries into I

In this case there are two aspectual morphemes as well as the inflection to be supported. The verb moves to the lowest one and cannot move further. Therefore two auxiliaries are inserted: be, determined by the progressive, is inserted onto the perfective morpheme which takes the phrase headed by ing as its complement, and have, determined by the perfective, is inserted onto the tense morpheme (in this case null) which takes the phrase headed by the perfective morpheme as its complement.

6.2.2 Do-insertion

Accepting this, we can account for the insertion of dummy do. The verb will not be able to move to inflection without violating the HMC. Apparently in English, the negative is not the sort of verbal element that can support tense and hence the only option available is to insert an auxiliary. As there is no aspectual morpheme to deem otherwise, the inserted auxiliary will be do:

6.2.3 Tense and Agreement

6.2.4 Movement to tense and I

6.3 Movement to Spec IP

We have said that the light verb which is responsible for assigning the Θ-role to the subject is responsible for assigning Case to the object. This seems to be the locus of Burzio’s generalisation that verbs which assign a subject Θ-role assign an accusative Case. Hence the object is in a Case marked position and need not move away in order to get Case. Consider the subject: why is it not in a Case position? Note that the verbal element above the subject, the tense in this case, does not assign any Θ-roles and hence its specifier position is empty at D-structure. Clearly this is unlike the light verb. We may propose therefore that tense is not an accusative Case assigning head. But why doesn’t the light verb assign Case to its subject? One might attempt to answer this by claiming that the light verb has to assign Case to the object and assuming that accusative Case can only be assigned to one place. While this seems reasonable, it doesn’t explain why the light verb taking an intransitive verb does not assign Case to its subject:

6.3 Movement to Spec IP

Presumably the agreement element is different in both these cases. For one thing, modal auxiliaries can appear in the agreement position of finite clauses, but not of non-finite clauses. Moreover, finite inflection selects for a finite tense headed phrase as its complement while the one in (63b) clearly selects for a non-finite complement. I will not have anything to say about the accusative Case of the subject of the non-finite clause at present, leaving this for future discussion. Instead, we will concentrate on the finite inflection, which assigns nominative to the subject.

6.4 Adjunction within IP

Note that the most natural position for these adverbs is after the modal but before the rest of the sentence, suggesting that it adjoins to the phrase headed by tense:

Chapter7 Complementiser Phrases

In this chapter we continue to present the parts of the English clause, extending it further upwards. So far we have seen that the clause has a number of layers to it, relating to certain syntactic and semantic properties. The lower layer consists of the thematic part of the VP, including the Θ-assigning light verbs, which concern argument and event structure. Above this we have the non-thematic part of the verb phrase where the morphemes of aspect and tense are introduced. Finally above this we have the IP in which agreement and modal auxiliaries are situated. The IP also provides the surface Case position for the grammatical subject.

7.3.3 Inversion

Looking at inverted auxiliaries, we see that they all have one thing in common: they are all finite. An inverted auxiliary may be a modal, which is inherently finite, or an aspectual auxiliary which bears tense and we never get a non-finite form of the auxiliary in the inverted position:

7.3.3 Inversion

The case of aspectual auxiliaries is similar to the modals. In the previous chapter we claimed that these auxiliaries are inserted elements that may move from the tense position to the I position when there is null agreement in I. Thus, if they are in I, they can also undergo movement from I to C:

7.3.3 Inversion

As we can see, a yes–no question involving a main verb moving to the C position is ungrammatical and instead of the main verb moving to C what happens is that the dummy auxiliary do is inserted into the tense position, and from there it moves to C, via I. Of course, this is readily accounted for if main verbs do not move to I, as is the standard assumption. If they are never in I they cannot move to C without violating the head movement constraint. But we argued that main verbs can move to I and so it is not readily apparent why they cannot move to C. We will put this issue to one side until we have discussed the facts about I-to-C movement more fully. For the time being, then, we will concentrate on I-to-C movement as it involves auxiliary verbs.

7.3.5 Subject questions

Before we consign (67c) to the waste bin however, let us see if it might be salvaged. We have argued that main verbs do not differ in their positions from auxiliary verbs except in the case of negation where the main verb cannot move over the negative head, but as auxiliaries are inserted into tense, the presence of negation does not affect them. Other than this, though, both main verbs and auxiliaries alike can occupy the I position (contra standard wisdom). If this is a general fact, then it is possible that main verbs can raise to C just as auxiliaries do and hence (68b) might be analysed as involving I-to-C movement of the main verb:

7.3.5 Subject questions

We have seen restrictions like this before. The adverb, for example must be above the verb and the negation must be above the verb but below the tense. It seems that the verb must be below the subject and hence when the subject is in spec IP the verb can be no higher than I. However, when the subject moves to spec CP the verb can move to C and still remain lower than the subject. When the verb cannot move from I to C there is no choice other than to insert the auxiliary do. However, it appears that the dummy auxiliary is not enough by itself to provide the wh-element with something to agree with, thus the auxiliary must be inserted in to tense and move from there to I and from there to C to provide enough semantic content to support the agreement. The verb stays behind in the VP:

7.3.5 Subject questions

The brackets around the condition in (71c) indicate that this seems to be a preference rather than a rigid condition and that if it is impossible for the adverb to both follow the tense and precede the verb, both are in the same place for example, then the condition may be relaxed.

Chapter8 The Syntax of Non-Finite Clauses

In this chapter we will concentrate on the non-finite clause and investigate syntactic phenomena that are exclusive to it. There is a surprising amount of this and the non-finite clause is a far more varied structure than its finite counterpart. Much of this variation concerns the subject which in many cases has connections with the verb selecting the non-finite clause as its complement. Thus the boundaries of the clause become blurred at this point. Most of the structures we will look at in this chapter are infinitives, which as they contain both a tensed element and a complementiser have the kind of structure we have been discussing over the previous chapters. Not all of them, however, have identical structures and the amount of functional structure they contain is one of the axes of variation between non-finite clauses. We end the chapter with a look at probably one of the strangest constructions in English, the gerund. This has been claimed to have a status somewhat similar to a mythical beast, being half one creature, half another. The gerund displays certain properties of clauses but also certain properties of DPs. This makes it a very interesting structure to analyse from the X-bar perspective which claims that the properties of a structure come from its head.

8.2.1 Raising

The verb will move from its original position to support some inflection, depending on what is present. If there are aspectual morphemes, the lowest will be supported by the verb, if not the verb will move to either the (null) tense, if there is a modal, or all the way to the I position if there is a bound agreement morpheme as well:

8.2.1 Raising

Here, the verb first moves to the tense position, and then into the I to support the bound tense and agreement morphemes. The subject in its D-structure position is Caseless, so it moves into the vacant specifier of the IP where it is assigned nominative Case.

8.3 The Gerund

The gerund from one perspective is a kind of non-finite clause inasmuch as it expresses something which is typically related to clauses, i.e. a proposition, and can contain elements such as aspectual morphemes which are related to some portion of the clause while excluding elements of finiteness such as tense and agreement (including modals). From another perspective the gerund is a nominal form and many of its properties are those of standard DPs. Thus, it is something which oscillates between clause and DP status.

8.3 The Gerund

However, such gerunds are standardly assumed to have PRO subjects and hence the subject position is not empty and we can account for why the determiner is impossible. In such gerunds we might suppose that the ing morpheme is added to the structure quite high, perhaps above the tense element. If we further assume that it is a non-finite tense which is responsible for assigning the Null Case borne by PRO we can account for why it is possible to have a PRO subject in a gerund.