In the following sentence (from here), is it grammatical to use subjunctive were instead of are?

As emphasized in a joke attributed to American philosopher Morris Raphael Cohen (1880–1947), logic texts had to be divided in two parts: in the first part, on deductive logic, unwarranted forms of inference (deductive fallacies) are exposed

Which one of the two moods sounds more natural after had to here?

Of Tense, Not Mood

The verb phrase “had to be di­vided” is not one of those whose
sub­or­di­nate clauses some­times take some­thing other than the
nor­mal in­dica­tive by some speak­ers and writ­ers and
oc­ca­sions.

Even if it were, there are no sub­or­di­nate
clauses here in your orig­i­nal.

That means what you are re­ally ask­ing about here is not mood but
tense; that is, whether the tense ought to use the nor­mally
in­flected present-ver­sus-pret­erite of be, so ei­ther the
plu­ral present are or else the plu­ral pret­erite were.

Per­haps it is both­er­ing you to see the present tense used later
in a sen­tence that first uses the pret­erite. If so, please see our
su­per-Fre­quently Asked Ques­tion en­ti­tled “He didn’t know where
New Jer­sey was”
along with its an­swers and those of its nearly four dozen linked
ques­tions.

Of Moods and Modes, and Their Marking

But if you still want some­thing gov­erned by what has some­times
his­tor­i­cally been called the “sub­junc­tive” by the more, ahem,
di­achron­i­cally in­clined mor­phol­o­gists and syn­tac­ti­cians,
but viewed syn­chron­i­cally is ac­tu­ally just a form of modal
mark­ing us­ing a “zero”-modal (bare in­fini­tive) or else by us­ing an ex­plicit
one like should or must, then here’s what you have to do...

To get some­thing fancier so that it’s “mod­ally” marked, you
would need to use a spe­cial verb like pro­posed or sug­gested
or in­sisted in the main clause so that you could mod­ally mark
some other verb in a new sub­or­di­nate clause gov­erned by the
main clause.

Ex­am­ple 1

Either by us­ing the bare-in­fi­ni­tive mo­dal­ity:

As a joke, Amer­i­can phi­los­o­pher Mor­ris Raph­ael Co­hen
pro­posed that logic texts be di­vided in two parts:

1. the de­duc­tive part where un­war­ranted forms of in­fer­ence are ex­posed
   


2. the in­duc­tive part where un­war­ranted forms of in­fer­ence are en­dorsed
   

Or by pre­fix­ing that bare-in­fi­ni­tive with an ac­tual modal verb:

As a joke, Amer­i­can phi­los­o­pher Mor­ris Raph­ael Co­hen
pro­posed that logic texts should be di­vided in two parts:

1. the de­duc­tive part where un­war­ranted forms of in­fer­ence are ex­posed
   


2. the in­duc­tive part where un­war­ranted forms of in­fer­ence are en­dorsed
   

Ex­am­ple 2

Either by us­ing the bare-in­fi­ni­tive mo­dal­ity:

As a joke, Amer­i­can phi­los­o­pher Mor­ris Raph­ael Co­hen
pro­posed that un­war­ranted forms of in­fer­ence be
ex­posed in the first part on de­duc­tion, and that they
be en­dorsed in the sec­ond part on in­duc­tion.

Or by pre­fix­ing that bare-in­fi­ni­tive with an ac­tual modal verb:

As a joke, Amer­i­can phi­los­o­pher Mor­ris Raph­ael Co­hen
pro­posed that un­war­ranted forms of in­fer­ence should
be ex­posed in the first part on de­duc­tion, and that they
should be en­dorsed in the sec­ond part on in­duc­tion.

On the Ab­sence of a Past Sub­junc­tive in Pre­sent-Day English

As you see, even if the main clause is in the pret­erite, the
sub­or­di­nate one is modally marked using just the bare in­fini­tive, never by using the
pret­erite or in the spe­cial, un­real were form for the unique
case of be.

This is an­other rea­son why call­ing some­thing “past sub­junc­tive”
in Pre­sent-Day English strains cred­i­bil­ity: we do not change
be to were, nor spend to spent, just be­cause the gov­ern­ing
clause is in the preterite.

We sim­ply use the bare in­fin­i­tive in all such sub­or­di­nate clauses, ir­re­spec­tive of the tense of the main clause.