[Music] we've seen that a transitive verb combines with two arguments the subject which frequently expresses the agent although not necessarily and the object which again not necessarily but frequently expresses the theme and we've also seen that these arguments are combined with a verb in a particular order so the verb combines first with the object and forms a constituent with that and then combine and then the result of that combines with the subject to form a larger constituent and we've also seen that we would want to associate or Express these selectional properties of the verb by representing in the Lexicon an elementary tree for the verb that shows these positions for the two arguments further as we've already discussed the properties of a phrase depend on the properties of the head so in this case since the head is a verb IT projects a verb phrase so in this more elaborate structure you can see that the lexical category of the head the V projects first to this larger constituent the V bar and then to an even larger constituent VP we've seen phrases of course that have heads other than V so we can have phrases headed by prepositions PPS or post positions also we've seen that you can have phrases headed by adjectives so you have adjective phrases we could hypothesize that phrases might all have a similar kind of structure the kind of structure we've just seen for the VP that hypothesis is sometimes called the xar schema so according to the xar schema all phrases have a similar structure to what we've just seen for the VP one way to represent that is to take a variable to stand for the actual lexical category so the head X which could be V or a will combine with one phrase and form a constituent xar so when V combines with its complement you get a v bar if an adjective combined with a complement you would get an a bar and then the resulting phrase combines with another phrase so the V bar combines with another phrase and you would get the VP or more generally an xar combines with another phrase and you get the XP so those two positions for phrases that are inside this xbar schema have names just for these positions so the complement of X is the sister to the head and then the phrase Which is higher up in the structure which is the sister to the xar is called the specifier so just to summarize a head an X projects two levels of phrase it projects to an X bar which can contain the head and its and the complement of the head and it can project further to the XP which would contain also the specifier so far we've seen this for verb phrases but you could come up with a possible hypothesis for the structure of noun phrases along the kind of lines that people have already been considering in class where a noun phrase would also have a head n in this case which would project an Nar which would contain also the complement of the the nominal head and then it will project further to an NP so that's one possible structure for nominal phrases as we've already discussed in fact there's Al an alternative way of looking at nominal phrases which is to to consider that rather than being projections of the noun they're projections of the determiner we'll be looking that in more detail later in that case the structure of a nominal phrase We would actually want to say that it's a DP because it's projected from the D rather than NP projected from the n and in the other diagrams that you'll see I've actually assumed that's the case so you'll see DPS everywhere but that's not important for the point here we're going to look at DPS and NPS later the point is just that this xar schema is intended as a General scheme for phrases of different categories as it stands it looks like that schema is not going to allow for all of the variety we've already seen in particular it seems in some cases it's going to give us too much structure so for example for although a transitive verb takes a complement as well as a subject we've seen plenty of cases of intransitive verbs which have subjects but no object objects so we'll assume that that complement position is actually optional and the specify position we can assume Also may be optional and so it will depend on the particular properties of the head whether it occurs with a complement and whether it occurs with a specifier there are also cases where it seems that the structure that we get from the expar schema isn't actually enough that we don't have enough positions within the phrase if that's all there is so two cases you could already think of are ditransitive verbs where you actually have three arguments to accommodate and also all these cases of modifiers that we've seen where it seems you have a an unlimited number of modifiers that can be included in a phrase we'll come back to ditransitive verbs in another class but uh we'll get back to modifiers very shortly this production is brought to you by the University of Edinburgh