21   Predicate noun phrases (NP-PRD)

The predicate noun phrase of a copular sentence is labeled NP-PRD. See section 9.4.6 for more details.

(224)
それはリンゴだった。

( (IP-MAT (PP (NP (PRO それ))
              (P は))
          (NP-SBJ *)
          (NP-PRD (N リンゴ))
          (AX だっ)
          (AXD た)
          (PU 。))
  (ID 821_aozora_Harada-1960))

NP-PRD is typically followed by the auxiliary verb (AX) such as だ and です, but in some instances the auxiliary verb is missing. In such instances, NP-PRD is followed by (AX *) to indicate that the AX is missing. For details on copula drop, see section 9.4.

(225)
「とってもきれいなガラス玉！」

( (IP-MAT (-LRB- 「)
          (NP-SBJ *pro*)
          (NP-PRD (IP-REL (NP-SBJ *T*)
                          (ADVP (ADV とっても))
                          (ADJN きれい)
                          (AX な))
                  (N ガラス玉))
          (AX *)
          (PU ！)
          (-RRB- 」))
  (ID 240_aozora_Yuki-1-2000))

(226)
ジョンはアメリカ人の外科医かもしれない。

( (IP-MAT (PP (NP (NPR ジョン))
              (P は))
          (NP-SBJ *)
          (NP-PRD (PP (NP (N アメリカ人))
                      (P の))
                  (N 外科医))
          (AX *)
          (MD かもしれない)
          (PU 。))
  (ID 1335_misc_JSeM_beta_150530))

     Formal nouns can head NP-PRDs. In some cases (most notably with はず) a following adnominal copula can take the form な, (normally a distingushing characteristic of ADJNs), but in all of these instances the formal noun is modified by a complement or a clause, necessitating an analysis of N. Some items (e.g., 病気) can appear in structurally ambiguous patterns (e.g., 病気の先生） used as either property-ascribing

     Note that so-called 「の」形容詞 are treated as nouns heading NP-PRDs. The recognition of copulas of the form の makes a principled description possible without dedicating a part of speech to these items.