The expletive "það" (tagged ES in all uses, including "weather" predicates - see ÞAÐ in Treatment of individual words) is sometimes not co-indexed with anything, as in weather expressions. This is identical to the treatment of expletive "it" in the English corpora for weather expressions like "it is raining". However, the Icelandic corpus differs from the English corpora in that "it"/"það" is always tagged with its own tag, ES, in expletive uses including weather predicates.
Það er byggilegt á Íslandi (literally 'It is buildable in Iceland').
( (IP-MAT (NP-SBJ (ES Það)) (BEPI er) (ADJP (ADJ byggilegt)) (PP (P á) (NP (N Íslandi)))))
Það rigndi í gær ('Yesterday it rained').
( (IP-MAT (NP-SBJ (ES Það)) (VBDI rigndi) (PP (P í) (NP (N gær)))))
There is also an empty expletive version of this. We insert (NP-SBJ *exp*) in sentences that would normally contain the overt expletive, (ES Það), but does not because the expletive has "disappeared" because of topicalization plus finite-verb movement (i.e. V2, i.e. V-to-C and embedded topicalization) or stylistic fronting. CAVEAT: We do *not* insert an empty expletive in every sentence that *might* have contained an overt expletive; the empty expletive is only inserted in clauses containing no other obvious overt subject. Therefore we do not insert the empty expletive in clauses with subject postposition and no overt expletive (because of topicalization/stylistic-fronting). This is true for postposition/extraposition of CP-THT-SBJ and IP-INF-SBJ, as well as for NP-SBJ (cf., for example, the sentence with "þykja" in IP-SMC).
This rule for when to insert an empty expletive differs from the English corpora (this is a true difference between Icelandic and English syntax), in that the empty expletive can also sometimes *not* be coindexed with something else in the clause. For example, the Icelandic corpus will contain instances of (NP-SBJ *exp*) that are the empty counterpart to weather-"það" or existential-"það", whereas the English corpora will not contain empty counterparts to weather-"it" or existential-"there".
( (IP-MAT (NP-SBJ *exp*) (ADVP-TMP (ADV enn)) (BEP er) (ADJP (ADJ byggilegt) (PP (P á) (NP (N Íslandi)))))
( (IP-MAT (CONJ en-en) (NP-SBJ *exp*) (NEG ekki-ekki) (VBP Á-EIGA) (NP-OB1 (N-NSAIC mál-mál) (D-PNSN ÞAÐ-SÁ) (CP-EOP (WNP-1 0) (IP-INF (NP-OB1 *T*-1) (TO að-að) (VB-TA dæma-dæma) (ADVP-LOC (ADV hér-hér)) (PP (P-D á-á) (NP (N-NSDIC þingi-þing))))))
Expletive coindexed with NP
( (IP-MAT-SPE (CONJ og-og) (NP-SBJ-1 (ES það-það)) (VBPI á-eiga) (ADVP (ADVR heldur-heldur)) (NP-1 (Q-N engin-enginn)) (NP-OB1 (PRO-A neitt-neinn)) (ADVP-LOC (ADV hérna-hérna)) (PP (P í-í) (NP (N-D sveit$-sveit) (D-D $inni-hinn))) (. ;-;)))
( (IP-MAT (NP-SBJ-1 *exp*) (PP (P Með-með) (NP (ADJ-D sama-samur) (N-D móti-móti))) (VBDI bar-bera) (RP til-til) (NP-TMP (D-A það-sá) (ADJ-A sama-samur) (N-A haust-haust)) (CP-THT-1 (C að-að) (IP-SUB (NP-SBJ (ONE-N einn-einn) (PP (P að-að) (N-D nafni-nafn)) (NP-PRN (NPR-N Márus-márus) (NP-PRN (N-N knífsmiður-knífsmiður)))) (VBDI hlaut-hljóta) (IP-INF (TO að-að) (VB missa-missa) (NP-OB1 (NP-POS (PRO-A sína-sinn)) (N-A ektavinnu-ektavinna) (NP-PRN (NPR-A Bersabe-bersabe))))))