Is "necesse" an adjective or an adverb

Question

Introduction

My enquiry arrises from a passage in “Lingua Latina Per Se Illustrata: Familia Romana” in its tenth chapter which is entitled “BESTIAE ET HOMINES” on its fifty-ninth line which is as follows.

"Spīrāre necesse est hominī."

The definitions of form I found are given below.

Dictionary Entries

1. A Latin Dictionary, 1962
   p. 1195, Adj.
   
2. Pocket Oxford Latin Dictionary, 2005
   p. 120, Adv.
   
3. Oxford Latin Dictionary, 2012
   vol. 2, p. 128, Adv.
   
4. Chambers Murray Latin-English Dictionary, 2016
   p. 457, Adj.
   

Android Applications

1. Collins Latin Dictionary
   Adj.
   
2. Whitakers Words
   Adj.
   

Enquiry

Can anyone provide a reasoned parsing of "Spīrāre necesse est hominī." which may be lent to a sense of whether "necesse" is likely to be an adjective or an adverb?

Answer 1

Lewis & Short, Gaffiot, Georges and Forcellini agree that it is an adjective. Oxford appears to be alone with its opinion that it is an adverb, and I wonder if the entry itself has anything to say about that. Aliquid alicui necesse est is a very common expression, and as Draconis has explained, a neuter adjective hardly seems out of place here.

But necesse is a very unusual adjective indeed. It is highly defective, i.e., most forms are never used; in fact, in classical Latin, necesse is the only existing form. It exists only in the neuter gender, and is only used in connection with the verbs esse and habere. (And even the latter is not all that common, I think.) It cannot be used attributively, i.e., you cannot say medicamen necesse accipio etc.

Therefore it is not particularly helpful to think of necesse as an adjective, because you cannot do most of the things with it that you could do with an adjective. Think of necesse esse as a fixed expression.

By the way, haud necesse est in figura necesse est in linguam Anglicam transferenda verbum "necessary" adhibere. "Must" aut "needs to" etc. satis est.

Answer 2

Spīrā-re necesse est homin-ī
breathe-INF necessary be.3SG.PRES human-DAT.SG
Breathing is necessary for a human.

I would call it an adjective without a qualm. It's linked to a nominal (an infinitive verb) by a copula, and that's a syntactic context that adjectives appear in:

Errā-re humān-um est
err-INF human-N.SG.NOM be.3SG.PRES
To err is human.

*Errā-re humān-ē est
err-INF human-ADV be.3SG.PRES
*To err is humanly.

Multē, magnopere, etc are also ungrammatical in that context.

Answer 3

I don't think it's productive to attempt to determine the part of speech of this word - it's neither, since it modifies neither a noun nor a verb. necesse/necessum est, opus est, ūsus est and oportet are all predicative expressions that are semantically indivisible, forming the predicate together. If you classify necesse as an adjective, you'd have to classify opus, ūsus as adjectives—afaik using magnum opus est to mean this is impossible, it will mean "the task is big", so you have to say valdē opus est— ...and then perhaps analyse oportet and the rest of Latin verbs as containing a head - the ending - stuck to an adjectival base (hey, there are plenty of languages where adjectives = verbs!). At least in my ignorance of generative syntax I don't see what would stop you. In short, here seems to be where traditional grammar becomes useless.

Pinkster's 2015 Oxford Latin Syntax Vol. 1 p. 622 suggests that these govern imperative argument clauses aka 'final' clauses since they regularly lack the subordinator ut (necesse est faciās ~ volō faciās), apparently with only a single instance of nē (surprising!).