Phrase structure rules like those introduced in Section 7.4 are very useful in describing the way that words are combined into larger units in a given language. However, they are not by themselves sufficient: we can very easily construct sentences that follow these rules but that are nevertheless not possible in English.<\/p>\n
Take a look at the following examples:<\/p>\n
These are all possible sentences of English, which is expected, given that they all follow the phrase-structure rule for VPs that we introduced in the preceding section:<\/p>\n
The verb phrase in (1a) consists of a verb without any of the optional phrases, the one in (1b) makes use of the option to include an NP, and the one in (1c) includes a second NP in addition.<\/p>\n
So, why are the following sentences not possible? After all, they also follow the rule in (2) \u2014 in fact, they have the same structures as the sentences in (1):<\/p>\n
We could argue that they are, in fact, possible but that, for various reasons, they simply don’t make sense. The sentence in (3a), for example, omits important information \u2014 it does not mention what<\/em> Noah handed to whom<\/em>. Conversely, the sentence in (3b) contains too much information \u2014 stumbling is something a person does by themselves, it does not involve another person.<\/p>\n However, these arguments quickly run into problems. Consider the following sentences:<\/p>\n The sentence in (4a) also omits important information \u2014 it does not mention what<\/em> Aylin drank. Nevertheless, it is a possible, perfectly normal sentence of English. When we hear (4a), we know that Aylin must have drunk something<\/em>, but we accept the omission and assume that the omitted information is not important. In the same way, when we hear (3a), we know that Noah must have handed something<\/em> to someone<\/em>, so why do we not accept this omission, even in a situation where the omitted information is not important? The sentence in (4b) contains too much information \u2014 walking is something that a person does by themselves, it does not involve a second person. Yet, we accept (4b) and interpret it to mean that Noah accompanied<\/em> Aylin home and that both of them walked. So why do we not accept (3b) and interpret it to mean that Aylin and Noah stumbled together, or that Aylin caused Noah to stumble?<\/p>\n Verbs simply differ with respect to the number of constituents that they can or must be used with. The meaning of the verb does not allow us to predict this number. Verbs also differ with respect to the type of constituent that they can or must be used with. For example, spill<\/em> must be used with a noun phrase referring to a substance that is spilled (for example, the water<\/em>), and it can be used with an additional prepositional phrase containing a noun phrase that refers to the location that this substance ends up in (for example, on the floor<\/em>). This is how it is used in (1b). The location cannot be expressed using a noun phrase instead, as in (3c).<\/p>\n The requirements of a verb concerning the number and type of constituents that it can or must be used with is called its syntactic valency<\/strong> (or sometimes its subcategorization<\/strong>). There are some types of valency that are so frequent that they have their own labels \u2014 verbs that do not require or allow any constituents (other than the subject), like stumble<\/em>, are called intransitive<\/strong>, verbs that require one noun phrase (in addition to the subject), like spill<\/em>, are called transitive<\/strong>, and verbs that require two noun phrases are called ditransitive<\/strong>. However, there are additional kinds of verbs \u2014 for example, verbs that require or allow a specific prepositional phrase, like look for<\/em>, or verbs that require a noun phrase and a prepositional phrase, like put<\/em> (Zoe put her phone in her pocket<\/em>).<\/p>\n It is therefore more useful to represent the valency of a verb by listing the number and type of phrase that it requires or allows. Before we try this, there are two issues to be discussed. The first is whether the subject should be included in such a list. Some linguists say this is unnecessary, at least in English, because all English sentences have a subject, so that nothing would be gained by including it. However, while all sentences<\/em> require subjects, not all verbs<\/em> do. For example, many weather verbs (like rain<\/em>, snow<\/em>, thunder<\/em>, etc.) do not require subjects, so when we use them in a sentence, we have to insert a meaningless it<\/em> in the subject position:<\/p>\n So it is best to include the subject (we will discuss another reason later).<\/p>\n Second, we have to distinguish between phrases that must<\/em> occur with a particular verb and phrases that can<\/em> occur with a particular verb \u2014 as we saw in the case of spill<\/em>, it has<\/em> to have a subject and one additional noun phrase referring to the material that is spilled, and it can<\/em> have a prepositional phrase referring to the final location of that material. Phrases that have<\/em> to be used with a particular verb are called its obligatory complements<\/strong>. Phrases that can<\/em> be used with a particular verb are called its optional complements<\/strong>. These differ from phrases that can be used with any<\/em> verb \u2014 these are called adjuncts<\/strong>. The following sentences illustrates the difference between optional complements and adjuncts:<\/p>\n On Monday<\/em> and in Paris<\/em> are adjuncts, as we could add them to any verb. You can see this by adding them to every single example sentence in this book \u2014 you will always get a possible (grammatical) sentence! Here are some examples:<\/p>\n In contrast, for her sunglasses<\/em> and over his notebook<\/em> are optional complements, as we can not add them to any verb. Again, try to add them to some example sentences from this book \u2014 this will not be possible most of the time. Again, here are some examples:<\/p>\n Optional complements must be included in valency descriptions, as they are specific to particular verbs, while adjuncts are, obviously, not included. Let us represent the valency of verbs as follows:<\/p>\n rain<\/em>: [ __ ]<\/p>\n<\/li>\n stumble<\/em>: [ NP __ ]<\/p>\n<\/li>\n walk<\/em>: [ NP __ ]<\/p>\n<\/li>\n drink<\/em>: [ NP __ (NP) ]<\/p>\n<\/li>\n watch<\/em>: [ NP __ NP ]<\/p>\n<\/li>\n see<\/em>: [ NP __ NP ]<\/p>\n<\/li>\n like<\/em>: [ NP __ NP ]<\/p>\n<\/li>\n hand<\/em>: [ NP __ NP NP ]<\/p>\n<\/li>\n spill<\/em>: [ NP __ NP (PP) ]<\/p>\n<\/li>\n\n