In this passage from Ars Poetica we find:
Ī́ncēptī́s grăuĭbū́s plērū́mque‿ēt mā́gnă prŏfḗssis
Pū́rpŭrĕū́s, lātḗ quī splḗndĕăt, ū́nŭs ĕt ā́lter
Ā́dsŭĭtū́r pānnū́s
I can't figure out if 'magna' is an adverb or a noun or if it is an adjective, which the OLD says it is, then what does it modify. In the LASLA database it says that 'magna' is a plural accusative modifying a neuter noun. I don't see any other nouns in this sentence which are plural accusative neuter. Here's the LASLA breakdown where the first column is the lemma, the second is the part of speech and the third is inflected form:
(The C in the part of speech pCd means any gender, though LASLA does not always get the gender right)
inceptum pNd inceptīs
grauis pCd gravibus
plerumque d plerumque_
et2 d et
magnus pna magna
profiteor pr.ac.pCd professis_
purpureus smn purpureus
late d late
qui1 smn quī
splendeo 3.pr.sj.ac splendeat
unus m unus
et2 d et
alter smn alter
assuo 3.pr.in.pa adsuitur
pannus sMn pannus
The Buckley, I think, translation has it as:
In pompous introductions, and such as promise a great deal, it generally happens that one or two verses of purple patch-work, that may make a great show, are tagged on.
