Here are my thoughts on those two questions of yours, maxsims:
1. Why is the past perfect not acceptable when a specific time frame is mentioned? I have never heard of such a rule.
You will recall that by definition, the past perfect in English is a verb tense formed with “had” to denote an action or state as completed at or before a past time spoken of. For example, “Rizal had written two novels by the time he turned 30 in 1891.” Here, the past perfect is used to denote an action whose time of occurrence isn’t specified (“had written”) but uses as referent another action in the past with a specific time of occurrence, “he turned 30 in 1891.” You know, of course, that the past perfect can’t be used in that sentence if the time of writing of the two novels is specified. We can’t say, “Rizal had written two novels between 1887-1890 by the time he turned 30 in 1891.” We can only use the simple past tense for both the first and second actions in such cases, like, say, “Rizal wrote two novels between 1887 and 1890, and this was before he turned 30 in 1891.”
The other use of the past perfect—and the one I referred to as commonly used in print journalism—is to indicate a past action whose time of occurrence isn’t specified at all, as in “Rizal had written two novels.” “Another presidential debate had been held.” Of course, when the time of occurrence is specified, the correct tense to use is the simple past: “Rizal wrote two novels between 1887 and 1890.” “Another presidential debate was held last January 31.”
2. By definition (perhaps not everybody’s), the subjunctive mood sets a notional, as distinct from a real or chronological, time. It follows that "...if he weren’t executed by the Spanish authorities in 1896 at the age of 35....etc” cannot be subjunctive.
As you know, the subjunctive mood denotes acts or states that are contingent on possible outcomes of the speaker’s wish, desire, or doubt, as opposed to denoting acts and states in real-world situations, which is what the indicative mood does, or to expressing direct commands, which is what the imperative mood does in turn. Here are two examples that I provided for the subjunctive in my book, Give Your English the Winning Edge:
“If the Earth were flat, Magellan’s naval expedition wouldn’t have circumnavigated the globe.”
“How I wish (that) I were here when she said that! I would have told her that she was a liar.”
Of course, such subjunctive constructions can sometimes take this inverted syntax:
“Were the Earth flat, Magellan’s naval expedition wouldn’t have circumnavigated the globe.”
The second subjunctive sentence above becomes so convoluted when its syntax is inverted, so we won’t attempt it here, but there are other similar constructions that allow the inverted construction without any hitch, like the following:
“Were she the CEO, our management wouldn’t be pursuing this erroneous course.”
These examples are applications of the subjunctive to describe the outcome of an unreal situation or idea contrary to fact.* They are actually of the same structure as the following subjunctive sentence of mine that’s in question here:
“Can you imagine, if he weren’t executed by the Spanish authorities in 1896 at the age of 35, how many more stories and novels he could have written—whether in Spanish, Tagalog, or English—had he lived to the ripe age of, say, 60 to 70?”
You will recall that I originally used the indicative “wasn’t” for that sentence, but when you indicated doubt about the usage in your posting, I decided to change it to “weren’t.” This was when I realized that the sentence should, in fact, be in the subjunctive form. It isn’t a very lovely construction actually, but that’s how it should be in the subjunctive form.
(Note that that sentence can also take this inverted subjunctive form: “If he weren’t executed by the Spanish authorities in 1896 at the age of 35, can you imagine how many more stories and novels he could have written—whether in Spanish, Tagalog, or English—had he lived to the ripe age of, say, 60 to 70?”)
What throws off a lot of people, of course, is the deviant behavior of the verb “be” in such subjunctive “if”-clauses. While both regular and irregular verbs in the subjunctive take the same form as their indicative past-tense forms (“worked,” “found,” “caught,” “saw,” and so on), “be” exhibits totally maverick behavior. It sticks to the past-tense subjunctive form “were” all throughout, regardless of the person and number of its subject: “She acts as if she were a member of royalty.” “They avoided the man as if he were a leper.” “The people behaved as if their future were a big joke.”
There’s actually a grammar rule that prescribes that if the situation described by the “if” clause is not false but actually happened, its operative verb should be in the indicative form instead, as in “If she was [not “were”] sick that week, then it’s obvious why she wasn’t able to attend her classes.” This was why I was tempted to use the indicative “were” in my original construction for that sentence of mine about Rizal:
“Can you imagine, if he wasn’t executed by the Spanish authorities in 1896 at the age of 35, how many more stories and novels he could have written—whether in Spanish, Tagalog, or English—had he lived to the ripe age of, say, 60 to 70?”
On second thoughts, however, I realized that the rule applies only to situations in the “if clause” that aren’t false or that actually happened, but the hoped for or imagined outcome is actually realized. In that sentence construction of mine about Rizal, though, both the “if” clause and the imagined outcome didn’t happen or have not been realized. This is why ultimately, I think the subjunctive “weren’t executed” and not the indicative “wasn’t executed” is the correct mood for that sentence of mine.
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*There are actually several other applications of the subjunctive that are discussed in my book, but I will limit this discussion to only this one so as not to unduly prolong this posting.