Convertible propositions

Ken Litwak  asked:
> 2.  What a convertible proposition is? (Rod Decker)

OK, my turn to be on the other end! The term is used in Dan Wallace's
_Exegetical Syntax of the Greek NT_ (Zondervan, forthcoming--see below)
along with a contrasting category: subset proposition. McGaughy's
_Descriptive Analysis of Einai_ doesn't use the term "convertible" (at
least a quick check didn't find it there) but he does discuss the same
construction using the term "interchangeable" (e.g., p. 68). 

Both terms describe one of two possible relationships between a subject
and a predicate nominative. The names are fairly transparent (better
choice than some of our technical terms!)--which is why Carl, and perhaps
others, were able to identify them correctly. A convertible proposition is
one in which the subject and predicate nominative are interchangeable.
"That is to say, both nouns have an identical referent. E.g., Jn. 20:31,
"IHsous estin ho Xristos"--interchanging the two may produce a somewhat
diff. emphasis, and the subj. should still be identified, but does not
change the meaning [maybe that shuld be rephrased in a more tech. way?]). 

A subset proposition is the more usual relationship that does not involve
interchangeability. "The predicate nominative describes the class to which
the subject belongs...S is a subset of PN." E.g., 1 Cor. 1:18, "ho logos
ho tou staurou...mwria estin," "'The word of the cross is foolishness'...
does not mean 'foolishness is the word of the cross,' for there are other
kinds of foolishness." Or 1 Jn. 4:8, 16, "ho Qeos agapH estin." To say
that "God is love" is quite different than saying that "Love is God." 

Here is a feeble, "ASCII art" attempt to present Wallace's diagram:
|       __________       |
|      | Subject  |      |   ___________     _____________
|      | ("John") |      |  |  Subject  |   | Pred. nom.  |
|      |__________|      |  | ("Jesus") | = | ("is the Son|
|                        |  |           |   |  of God")   |
|  Predicate nominative  |  |___________|   |_____________|
|     ("is a man")       |
   Subset proposition           Convertible proposition

To address the question as to how these two types of sentences may be
distinguished, Wallace proposes the following rules (which I have adapted
a bit--see the preceeding thread on Phil. 2:13--and in light of the
responses [which I appreciate very much], should probably be honed some
more); as Wallace's grammar states them, but without the examples: 

1. The subject will be a pronoun, whether stated or implied in the verb.
2. The subject will be articular.
3. The subject will be a proper name.

When only one nominative substantive has such a grammatical "tag," the
semantic relationship will be that of particular (subject) to class
(predicate nominative). That is, the construction will be a subset

If both S and PN have one of these three tags, the following "pecking
order"  applies: 

1. The pronoun has greatest priority: it will be the S regardless of what 
grammatical tag the other substantive has.

2. Articular nouns and proper names apparently have equal priority. In
instances where one substantive is articular and the other is a proper
name (or where both are articular), word order is the determining factor. 

The semantic relationship is such instances is that of a convertible 
proposition. That is to say, when both substantives meet one of the three 
qualifications for S, then they become interchangeable.

---end of material from Wallace---

Most of you will never have seen this grammar since it has not yet been
published. I'm using a draft copy as part of a pilot program in teaching
second year syntax this year. It is tentatively scheduled to be available
for fall 95 use. My opinion of it thus far is highly favorable for use as
a reference tool.  It is aimed at the intermediate grammar level (a la
Dana and Mantey), but in actuallity it falls between D&M and Robertson--
prob. closer to Robertson.  That makes it (IMHO) a less than desirable
choice as a _textbook_ for second year syntax courses--too much detail and
too many technicalities; but a much more accessible reference tool than
BDF or Moulton and more up-to-date than Robertson. My guess is that for
the typical pastor who uses Greek (is that animal typical?! that's my goal
teaching Greek in a seminary context) it will be all he will need for most
purposes if combined with his first year grammar and a good intermediate
grammar (my recom. for that is Porter's [surprise!] _Idiom's of the Greek
NT_--a grammar much better suited for _textbook_ use in second year
syntax. So, keep your eye on Zondervan's catalog next summer and start
saving your money. The draft I have is over 400 laser-printed,
single-spaced pages--and there are one or two major sections that are only
sketched in at this point [at least in the draft ms]--it prob.  won't sell
for $19.95! For those of you who teach, be thankful that Zondervan has one
of the most generous examination copy policies in the industry: _free_ if
it relates to what you teach. 

As to Ken's second question:
> I'm left unsure how to doescribe what each tense is for, since  
> they all seem so fluid -- if they don't point to time, does any 
> of them truly have a distinctive meaning?

I've already used my share of space here on that subject. Read the
previous thread s.v. "aspect" for details. Else get Stan Porter's _Idioms
of the Greek NT_ and check his section on verbs. (If anyone is curious,
send private email and I'll send you a copy of the 16-page "Intro. to
Verbs and Verbal Aspect" that I used in 2d year syntax this fall.)

Rod Decker
Calvary Theological Seminary