How can participles (inflected forms) be distinguished from deverbal adjectives (derived forms) in Latin?

Question

Many modern linguistic analyses of languages like English draw a sharp theoretical distinction between participles, which are analyzed as inflected forms belonging to the paradigm of some verb, and deverbal adjectives (also called verbal adjectives, participial adjectives, or departicipial adjectives), which are seen as adjectives derived from verbs. (There are certainly disputes about the validity of the inflection/derivation dichotomy, but it nevertheless seems to have wide acceptance. There are also disputes about whether participles should be analyzed as verbs, adjectives, neither or both, but I don't think that's as relevant to my question. Also, the word "participle" is often used in a broad sense that covers both an inflected form and a derived word with an identical form, but the broad vs. narrow definitions of "participle" just seem to be a matter of terminology.)

However, it can be tricky to determine which category a word belongs to in a specific example sentence. There are some syntactic tests, but often they only work in particular situations and can only give a definite answer in one direction. (E.g., in English, if an -ing word has a direct object, that is considered to be proof that it is a participle and not a deverbal adjective, but if it doesn't have a direct object, it might be either a participle or a deverbal adjective. If an -ing word is modified by the word very, that is considered to be proof that it is a deverbal adjective and not a participle, but if it is not or cannot be modified by the word very, it might be either a participle or a deverbal adjective.)

I would like to know about any such syntactic tests that have been noted or proposed for distinguishing Latin participles (in the sense of "inflected forms") from derived adjectives.

Answer 1

Since posting this question, I have found some information, although I'm not as sure of it as I would like to be. I use some hedging in this answer, but this is only meant to indicate my personal lack of certainty; I'm not saying that the matter is objectively uncertain.

Possible syntactic differences

-ns words may only take accusative direct objects when they are participles

Apparently, in Latin, as in English, a verbal active participle can take a direct object in the accusative case, but a departicipial adjective typically can't. I asked a separate question about this topic: When are -ns words used with accusative direct objects?

Adjectives, but not participles, can take comparative morphology

Joonas Ilmavirta asked a question about Comparison of participles. Based on the current answers, it seems that the use of comparative or superlative morphology is typically viewed as a sign that a word is a departicipial adjective rather than a true verbal participle.

Possible morphological differences

negation with non for participles vs. negation with in- for adjectives

The following information doesn't help much to distinguish participles from adjectives when a word is not negated, but it seems relevant to the overall question of whether Latin distinguished verbal and adjectival participles:

in Classical Latin the synchronic negative of e.g. patiens ‘enduring’ is non patiens, whereas participles with a negative prefix are synchronically non-participial adjectives, e.g. impatiens ‘impatient’.

(p. 30, "Negated Participles in Ṛgvedic Sanskrit and Proto-Indo-European," by John J. Lowe, Indo-Iranian Journal 54 (2011) 19-38)

-ns participles and adjectives might inflect differently in the ablative

Bennett's Latin Grammar says

Participles in -ans and -ens follow the declension of ĭ-stems. But they do not have -ī in the Ablative, except when employed as adjectives; when used as participles or as substantives, they have -e; as--

ā sapientī virō, by a wise man ; but
ā sapiente, by a philosopher
Tarquiniō rēgnante, under the reign of Tarquin

("Adjectives of the Third Declension", §70 "Adjectives of One Termination")

However, it seems that this is at best a simplification, at worst a misrepresentation of the usage of these two forms. In "Declension of the Latin present participle in connection with its syntactico-semantic use" (2018), Hendrik Christiaan Walvoort says "I conclude that a twofold declension paradigm of the ppa according to syntactico-semantic use is only mentioned in the sixth/seventh century by the anonymous author of the Ars Ambrosiana, but not by the ancient and the other medieval grammarians" (§3). Even if it is a real rule, there are apparently many exceptions, so inflection is not a reliable way of distinguishing verbal participles from adjectives.