Why only 1 complement is possible?

Question

_{Source: p 178, 179. Syntax, A Generative Introduction (3 ed, 2012) by Andrew Carnie}

[p 178:] 81) Adjunct rule: X' ⟶ X' (ZP)
82) Complement rule: X' ⟶ X (WP)

[p 179:] What this means for complements and adjuncts is that you can have any number of adjuncts (87), but you can only ever have one complement (88): [...]

Why not a Noun Phrase with multiple equipollent Prepositional Phrases?

I saw this on Reddit, and someone commented

The theory that Carnie is using makes a number of assumptions -- most of which are no longer assumed by most linguists -- and then juggles everything to make sure that these assumptions are not violated by any analysis. This results in a lot of messy non-terminals, many of which are empty and useless; these come with a Do Not Remove Under Penalty Of Law sticker in a textbook.

Examples. I embolded the multiple complements.

1. On The Road by Jack Kerouac. 1957.

“The only people for me are the mad ones, the ones who are mad to live, mad to talk, mad to be saved, desirous of everything at the same time, the ones who never yawn or say a commonplace thing, but burn, burn, burn like fabulous yellow roman candles exploding like spiders across the stars.”

7 of the Most Memorable Long Sentences In Lit — Barnes & Noble Reads

“For Heaven only knows why one loves it so, how one sees it so, making it up, building it round one, tumbling it, creating it every moment afresh; but the veriest frumps, the most deject of miseries sitting on doorsteps (drink their downfall) do the same; can’t be dealt with, she felt positive, by Acts of Parliament for that very reason; they love life. In people’s eyes, in the swing, tramp, and trudge; in the bellow and uproar; the carriages, motor cars, omnibuses, vans, sandwich men shuffling and swinging; brass bands; barrel organs; in the triumph and jingle and strange high singing of some aeroplane overhead was what she loved; life; London; this moment of June.” —Mrs. Dalloway, by Virginia Woolf.

“There was a wisteria vine blooming for the second time that summer on a wooden trellis before one window, into which sparrows came now and then in random gusts, making a dry vivid dusty sound before going away: and opposite Quentin, Miss Coldfield in the eternal black which she had worn for forty-three years now, whether for sister, father, or nothusband none knew, sitting so bolt upright in the straight hard chair that was so tall for her that her legs hung straight and rigid as if she had iron shinbones and ankles, clear of the floor with that air of impotent and static rage like children’s feet, and talking in that grim haggard amazed voice until at last listening would renege and hearing-sense self-confound and the long-dead object of her impotent yet indomitable frustration would appear, as though by outraged recapitulation evoked, quiet inattentive and harmless, out of the biding and dreamy and victorious dust.” —Absalom, Absalom!, by William Faulkner

Answer 1

The problem you point to is addressed later in Carnie's book, starting on page 412. The greater issue concerns the extent to which tertiary branching should or should not be assumed. This matter splits the syntax community. See the discussion of strictly binary branching structures here.

A main trait of the X-bar schema as it is commonly understood is that it allows binary branching only (which is sometimes abbreviated down to unary branching when no specifier is present). If you flip through Carnie's book, the trees you see almost all involve binary branching; there are no tertiary branching trees (except when conjunction is involved). These strictly binary branching structures are widespread in modern frameworks of syntax. They are, though, controversial. My personal view is that they are not well motivated precisely for the reason you point to. Tertiary branching is needed when a head takes two complements (or perhaps three) instead of none or just one.

The particular issue you point to concerns ditransitive verbs. These verbs take two complements instead of just one, e.g.

(1) Josh gave Clay the book.

In this example, a tertiary branching structure appears to be needed, one in which both Clay and the book are shown as complements of gave. If all branching is strictly binary, though, then it's impossible to accommodate the fact that both Clay and the book should be immediate dependents of gave. To overcome this difficulty, X-bar theoretic syntax tends to assume VP-shell analyses. That is, they posit one or more additional head categories and assume leftward movement up the tree of the head verb. See the trees on pages 422 and 423 of Carnie's book. By positing more than one head position for the verb, multiple complements can be accommodated. The resulting trees are very tall indeed, but they seem scientific insofar as they are regular, all branching being beautifully binary.

Many of us in the syntax world view these strictly binary branching analyses with skepticism. I do not think they are well-motivated empirically. Quite to the contrary, the results of many tests for constituents reveal that tertiary branching structures are often present. I therefore encourage you and anyone reading this answer to question and challenge those strictly binary branching analyses of syntactic structures. Demand empirical evidence for their existence.

Concerning the examples you point to from famous authors, I do not think they involve multiple complements in the way suggested by your question. They appear, rather, to be cases of asyndetic conjunction and/or ellipsis instead.