What are the theoretical reasons for treating the preposition as the head of a prepositional phrase? (Noun as head of NP sounds fine intuitively, but the same does not apply to prepositions in prepositional phrases. I have never seen a theoretical justification for this treatment.)

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    If the head of an NP is a noun, and the head of an AdjP is an adjective , and the head of an AdvP is an adverb, and so on, why shouldn't a preposition be the head of a PP? – BillJ Oct 22 '18 at 15:35
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    That does introduce a rather different concept of "head" -- in an NP or VP, one can refer to the N or V alone, and it defines the constituent. In a PP, the important word is the NP object, not the preposition. PPs act like NPs in many ways and calling them something different doesn't change that. Headship is another weak point of this theory. – jlawler Oct 22 '18 at 15:46
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    And we can equally refer to the P alone, which defines the phrase. Prepositions take a wide range of complement types comparable to that of verbs: "I was talking to a friend" (NP Object); "I regard her as a friend" (predicative); "I stayed until after lunch" (PP) ; "It won't last for long" (AdvP); "I left because I was tired" (clause). We could hardly claim that all those PP resemble NPs. The important word is the prep, since that is that word that takes the dependents in the same way as the head does in other categories. – BillJ Oct 22 '18 at 17:51
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    jlawler has hit the nail on the head. Take out the adnominal elements (excluding articles) and you still have a viable NP. "I felt the overpowering heat that emanated from the alien spaceship" > "I felt the heat". But take out the other elements of a prepositional phrase and you mostly get nonsense. "I was talking to" (really?), "I regard her as" (?), "I stayed until" (?), "It won't last for" (?), "I left because" (?). The prepositions are an element shared by all prepositional phrases, but without the rest of the phrase prepositions are mostly just flotsam. – Bathrobe Oct 23 '18 at 10:57
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    "That" is a meaningless subordinator, but preps have a semantic content, and hence make a contribution to the meaning of the PP. – BillJ Oct 23 '18 at 17:01

The head of a phrase ought to affect the category of that phrase. In turn, we can estimate whether phrases are of different categories by examining facts of verb subcategorization. Paradigms like

   He fell into the hole
  *He fell the hole.  

suggest that "into the hole" and "the hole" are of different categories, which will be true if the preposition "into" is the head of the complement of "fell", but not necessarily otherwise.

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    Answer makes sense. The 'head' of a 'phrase' is the word that determines the syntactic category of the phrase. OK. But this sounds like a labelling exercise. NPs are endocentric whereas PPs are not. Quite a difference. Prepositions also somehow strike me as a superficial phenomenon. Take 'I was there in June' vs 'I was there until June', both with PPs (except in journalism), but 'I was there last June' vs 'I was there until last June' or 'I was there yesterday' vs 'I was there until yesterday'. It may be linguistically relevant to signal PPs vs non-PPs, but the distinctions seem skin deep. – Bathrobe Oct 23 '18 at 12:34
  • In logical notation, prepositions are usually ignored, especially if they're governed by the verb as transitivizers, like the at in look at or the to in listen to. Logically, those are transitive verbs; syntactically, they're not even constituents. But logic is strong enough to make idioms -- Lookit! – jlawler Oct 23 '18 at 17:04
  • @jlawler, If "look at" and "listen to" are not constituents, how come they can be passivized or gapped as though they were verbs? – Greg Lee Oct 23 '18 at 17:24
  • Because the morphology has run them together to become new complex verbs. That's how new constituents come about. It also means that they have two constituent structures simultaneously; either can be chosen. As the OP suggests this is a labelling exercise. Me, I don't believe in heads as a formal category, just a loose associative term. – jlawler Oct 23 '18 at 18:06
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    "Head" is not a category; it's a function term. Complex verbs? The verbs in "look at" and "listen to" are 'prepositional verbs, i.e. the prep is specified by the verb. – BillJ Oct 23 '18 at 18:15

Heads are useful for understanding deep structure, but they can be hard to identify in surface structure.

  • Heads are closed-class words -- they are difficult to coin.

  • Heads have default values, which can often be elided if doing so will not confuse the delineation of other phrases.

  • Languages are pretty consistent about whether heads append to the beginning or end of phrases.

That said, nouns would not be the heads of phrases. The head of an NP would be a quantifier, but it can be omitted if the noun is proper, or the quantity is '[all]', or the quantity has been mentioned (definite). That is why some theories use DP instead of NP (and determiners don't have to also be pronouns).

Temporal nouns used adverbially don't need a head (preposition) because it can be assumed ('Sunday' = '[at] Sunday' = 'on Sunday') or it has already been grafted onto the noun ('today').

Verbs are headed by auxiliary verbs, unless those are omitted for the default (habitual/present tense or irregular verbs) or have been morphed onto the verb (regular past tense).

  • That is a GG explanation in terms of tree diagrams, and, I would suggest, potentially just an artifact of the theory. What I asked for was a theoretical justification for the notion that prepositions head PPs. Also, how cross-linguistically relevant is the PP? Are all languages supposed to have them? – Bathrobe Nov 23 '18 at 8:56
  • Whether to call them 'heads' or 'tails' is just an artifact, but the theoretical justification is that lexical words are stored only once, in a dictionary, and all storage of event memory is done only with heads (function words) that link (to other heads or finally to the lexical dictionary). The theory (not yet a "theorum" per Richard Dawkins) says that the closed-class distinction is important and will be observed in the brain. ... – amI Nov 23 '18 at 17:02
  • I don't know whether a 'prep' is the only way to express a relation between objects, but I suspect that the chaining of heads ("would have been on") may be an artifact of the abstract 'tree' rather than a feature of the concrete 'net'. – amI Nov 23 '18 at 17:02
  • The additional explanation is helpful and answers my question. Your disclaimers are important, though, particularly the fact that the theory assumes the function vs lexical distinction is observed in the brain. One could uncharitably assume that this is more a pious hope than a proven fact. – Bathrobe Nov 25 '18 at 7:10
  • Indeed -- Information entropy says we won't find overly redundant data in the brain, but whether the data is overt and orthogonal, or covertly hidden in layers, (or something spookier), is as yet unknown. – amI Nov 25 '18 at 16:51

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