Only verbs with modal meaning that take bare infinitives are tagged as MD:
mega 'may', munu 'will', skulu 'shall', vilja 'want, will'
VILJA does not always function as a modal; e.g. in cases where it takes a direct object, it is not tagged MD: Ég vil þetta. There is considerable variation in earlier texts as to whether VILJA takes að-marked infinitives or not, and individual texts/authors are not expected to be consistent in this (occasionally this happens with SKULU as well, and very very occasionally with MUNU: see Ævisaga Jóns Steingrímssonar for MUNU as VB). For this reason, we tag VILJA as MD when it takes a bare infinitive, and as VB elsewhere. Analysts are cautioned to look for both taggings of VILJA in studying the history of Icelandic modals!
Verbs with modal meaning that take að-marker (to) and an infinitive are not tagged as MD but as main verbs taking IP-INF:
eiga 'ought to', fá 'be allowed to', hljóta 'must', kunna 'can', þurfa 'need to', verða 'must', ætla 'intend'
KUNNA can (rarely) take a bare infinitive, in which case it may be ambiguous between being a modal and being equivalent to "be able to VB" with an IP-INF complement (see Ævisaga Jóns Steingrímssonar and Jón Indíafari for examples). In this case, we continue to tag it VB and treat it as taking an IP-INF complement.
If a verb that usually takes the að-marker for some reason does not, and does not have modal meaning, it is still parsed as taking IP-INF.
( (IP-MAT (NP-SBJ (PRO-A Hann-hann)) (VBPI langar-langa) (IP-INF (VB fara-fara))))
Infinitive of some pretero-present has a special past marking (Hann sagðist mundu/skyldu gera þetta). This is not tagged especially: we tag it as MD and not MDD.
Verbs elided after modals
See PPCEME guidelines.
VB before VB*
When a verb is fronted and becomes before a finite verb other than a modal, parse it as IP-INF.
(ADVP-TMP (ADV þá-þá) (CP-REL (WADVP 0) (C er-er) (IP-SUB-SPE (IP-INF-SPE (VB nálgast-nálgast)) (VBDI tók-taka) (NP-SBJ (NP-POS (N-G fyrirheits$-fyrirheit) (D-G $ins-hinn)) (N-N tími-tími)))))