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What is a theta role? Is it the same as a thematic role?

And what does it mean for a theta role to be undischarged/unsaturated? I came across these terms in a syntax paper. It seems like both undischarged/unsaturated were referring to the same effect. It might help to know what it means for a theta role to discharge/become saturated, and how it happens to discharge/become saturated.

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  • The answer to the first part ("what is a theta-role?") can easily be found with a Google search. The second part ("undischarged/unsaturated") requires only a bit more effort. Could you be more specific? What do you already understand about the subject and what is still unclear to you? – Otavio Macedo Nov 9 '11 at 18:18
  • I guess I came across the term "undischarged" theta role. The next sentence, in what seemed to be referring to the same phenomena, I came across "unsaturated" theta role. It seems like they refer to the same thing, I wasn't sure what it meant for it to be unsatured/undischarged. I knew a tiny bit about theta roles -- that they are similar to thematic roles. Wasn't sure if there was a difference between them -- based on the one answer, it seems that they are (mostly) synonymous, which is what I had assumed. – user325 Nov 9 '11 at 19:08
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    And yes, I know it's a pretty basic question -- but, hopefully, it will help someone else who might be searching for information on theta/thematic roles and terminology related to them. – user325 Nov 9 '11 at 19:14
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There is a syntactic notion and a very closely related semantic notion of "thematic role" that are more or less meant to map onto one another. Essentially, a theta role is the label for how the referent of an NP acts in the event the sentence describes. So, in "John ate an apple", John is the eater, and the apple is the eatee. In linguistic theory we think we've come up with "general" theta roles that are what the syntax care about -- the eater in "John ate an apple", the kicker in "John kicked the ball" etc are "agents", the eaten thing and the kicked thing are the "patients". Mark Baker has proposed -- and it has been pretty standardly assumed to be true in Chomskyan syntax -- that these theta roles are tied to particular positions in the syntax (which is why "John loves Mary" and "Mary loves John" mean different things!). Theta theory says that each verb comes predetermined with a certain number of theta roles, and each theta role must be assigned to one and only one NP. That's why "John loves" doesn't mean the same thing as "John loves himself", and why "*John arrived Mary" isn't acceptable ("arrived" doesn't have an object theta role).

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    Note too that on some theories at least, it's not just verbs that assign theta roles. For instance, sometimes you'll see it claimed that nouns have a "possessor" theta role. – Leah Velleman Nov 9 '11 at 18:37
  • Theta theory has lots of problems, e.g. how theta roles are assigned with reflexive verbs, John and Mary kissed, etc. What about weather verbs, e.g. it snowed? – Alex B. Nov 9 '11 at 19:35
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    Also, notice the title of a part of Heidi Harley's 2011 paper, 19.2 A minimal theta-theory: None [emphasis mine - Alex B.]. The paper itself is called "A minimalist approach to argument structure"; it's chapter 19 in The Oxford Handbook of Linguistic Minimalism. – Alex B. Nov 9 '11 at 21:12
  • Yes :) There are some who have claimed that theta roles are largely redundant with independently motivated things. My personal favorite is Borer's argument in her 2005 books that theta roles are completely subsumed by event structural notions such as "originator" and "delimiter", and that those seem to have some principled positions in the syntax. But, especially when trying to understand things like control and raising, the GB-style theta role theory seems to be the most sensical way of thinking about things. – dustinalfonso Nov 10 '11 at 16:48
  • Thank you for all the related information, Alex B., dustinalfonso, and Dan Velleman. I am going to read up on some of these minimalist approaches which sound quite interesting. – user325 Nov 11 '11 at 22:47
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Theta role ≠ thematic role.

The term ‘thematic role’ is used fairly often in linguistic description to label the class of things like ‘agent’, ‘patient’, ‘goal’, ‘experiencer’, ‘instrument’, and so forth. These are semantic properties that most people take to be assigned by the verb or by adpositions to the various noun and adposition phrases occurring in the clause.

In English, the subject of an ordinary transitive verb usually receives the agent role, thus in ‘I hugged her’ the subject ‘I’ is the agent that does the hugging. But if the verb is passivized then the subject gets the patient role instead, thus in ‘she was hugged by me’ the subject ‘she’ is the patient. So thematic role (agent, patient, etc.) and verb argument (subject, object, etc.) are not identical.

The concept of theta role is basically limited to theories that descend from Government and Binding (GB). Other folks here have discussed it above so I’ll skip describing it. It arose from the concept of thematic roles, hence the use of the Greek letter θ. The idea of numbering them, as done in various flavours of GB, is due to Relational Grammar (RG) I believe. RG is also the source of the terms ‘unaccusative’ and ‘unergative’, describing the alignment of subjects of intransitive verbs with either agent or patient thematic roles and hence the syntactic consequences. (I think Geoff Pullum ranted about this in his Topic...Comment column under the heading “Citation etiquette beyond Thunderdome”.)

The idea of ‘saturating’ or ‘discharging’ a theta role is that on the one hand the verb has some theta roles to hand out to noun phrases, and that the noun phrases are sitting around waiting to get a theta role. If a verb ends up with extra theta roles, or if a noun phrase doesn’t get a theta role, then the sentence is ungrammatical (or its derivation ‘crashes’ in Minimalist terms). So noun phrases have theta roles that need to be saturated, and verbs have theta roles that need to be discharged. There are a couple of other terms such as ‘fulfilled’ and the like that are also used for the same phenomenon.

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