Remember than infinitives are “typically frozen case-forms” of verbal nouns (Fortson 2010: 107; see also Weiss 2009: 445). So, in several IE branches (Balto-Slavic, Indo-Iranian and Italic), there is a “specific infinitive formation often called the supine that is solely used with verbs of motion to indicate purpose” (Fortson 2010: 108).
In Latin, it’s also ...
The supine is, in fact, the remnant of a fourth-declension nominal form, a verbal noun which stood for the action itself. The Plautine comedies still record an intermediate stage of this syntactical use.
For example, we have accusative with ire, as in ire obsonatum "to go shopping" or ire venatum "to go hunting". On the other hand, redire takes the ablative,...
Looking at it, I don't think me is ablative; it's more likely an accusative as the subject of an indirect statement with credere. Discessu here is not a supine, but a fourth-declension noun, discessus.
The translated line should actually be:
Nor did I believe that I in my departure would ever have caused you so much pain.
(Apologies for the tenses.)
Supine means flat on your back, lying down, It is the final 'oblique' form; it is the extremely inflected (leaning) part of the Verb and is usually in the last column of the principal parts,
In later Grammars (that certainly includes medieval Grammars) 'oblique cases' and 'declension' are only used to describe the Voc., Acc., Gen., Dat., Abl., Loc., (X ...
I think that the straight answer to the title question is 'No'.
The supine is not exactly the most frequently found verbal form. The accusative form, as far as I know, is used only to indicate the objective of the main action after verbs of motion, and the ablative (the only other case found, though it is sometimes described as dative) only to qualify an ...
The main difference between the supine and the future participle, as I see it, is that the supine is unambiguous about its expression of purpose, whereas the future participle allows for a wide range of meanings, of which purpose/intention is one. Allen & Greenough (§499) give this summary of the range of meanings (with examples):
Likelihood or ...
The second supine (ending with -u) can only be combined with adjectives, or with fas and nefas. Examples:
iucundum cognitu atque auditu
nefas est dictu
A second supine verb never has an object, but it can have a subject, for example pleraque faciliora sunt dictu quam factu.
Although Tom Cotton's answer may be correct for pure Classical Latin, it neglects other eras of the language.
Excerpted from W. M. Lindsay's Syntax of Plautus 5.42 (emphasis mine):
The Verbal Noun in -tus (4th Declension) is greatly in evidence in Plautus. We find the Accusative with eo, etc., e.g.
ire obsonatum to go a-marketing,
ire venatum to go ...
Yes, there certainly is a difference, which is that between adjective and noun.
There are several ways to express a purpose. Beginning your sentence with Romam venit, you might use the following:
. . . . me salutatum — the supine accusative (used like an infinitive after a verb of motion)
. . . . ut me salutaret — final clause with ut + subjunctive
. . . ...