I'm used to the which-hunters' ill-informed prejudice against the traditional role of which in integrated relative clauses (discussed here, here, here, here, here, and in many other LL posts over the years). But I now learn that some extremists have targeted which even in its grammatical ghetto of supplementary relative clauses, ("Why are some summatives labeled 'vague'?", 5/21/2008; "More theory trumping practice", 5/22/2008.)
The endangered examples of supplementary which are those that have a "summative" function, "understood as referring to some situation or proposition alluded to in the preceding discourse". A simple example: "Neptune opposes Apollo, which implies that things moist and dry are in continual discord."
That example, which is classical as well as simple, comes from Alexander Pope's side note on verse 91 of book VIII of the Iliad:
With what Art does the Poet engage the Gods in this Conflict! Neptune opposes Apollo , which implies that Things moist and dry are in continual Discord: Pallas fights with Mars , which signifies that Rashness and Wisdom always disagree: Juno is against Diana , that is, nothing more differs from a Marriage State, than Celibacy: Vulcan engages Xanthus , that is, Fire and Water are in perpetual Variance. Thus we have a fine Allegory conceal'd under the Veil of excellent Poetry, and the Reader receives a double Satisfaction at the same time from beautiful Verses, and an instructive Moral.
It's easy to find other examples of summative which in the works of great writers over the centuries. Shakespeare was so fond of it that in the first three plays I checked, I found a summative which in Act I, Scene 1. Thus Henry IV, part 1:
This is his Vnckles teaching. This is Worcester
Maleuolent to you in all Aspects:
Which makes him prune himselfe, and bristle vp
The crest of Youth against your Dignity.
And A Midsummer-Night's Dream:
Be it so she will not here before your Grace
Consent to marry with Demetrius,
I beg the ancient privilege of Athens,
As she is mine, I may dispose of her:
Which shall be either to this gentleman
Or to her death, according to our law
Immediately provided in that case.
And As You Like It:
Yet he's gentle; never schooled, and yet learned; full of noble device; of all sorts enchantingly beloved; and indeed so much in the heart of the world, and especially of my own people, who best know him, that I am altogether misprised: but it shall not be so long; this wrestler shall clear all: nothing remains but that I kindle the boy thither; which now I'll go about.
We expect that a writer of complicated prose like Laurence Sterne will use summative which, like this example from Tristram Shandy:
Yorick was this parson's name, and, what is very remarkable in it, (as appears from a most antient account of the family, wrote upon strong vellum, and now in perfect preservation) it had been exactly so spelt for near,—I was within an ace of saying nine hundred years;—but I would not shake my credit in telling an improbable truth, however indisputable in itself;—and therefore I shall content myself with only saying,—It had been exactly so spelt, without the least variation or transposition of a single letter, for I do not know how long; which is more than I would venture to say of one half of the best surnames in the kingdom; which, in a course of years, have generally undergone as many chops and changes as their owners. —Has this been owing to the pride, or to the shame of the respective proprietors? —In honest truth, I think, sometimes to the one, and sometimes to the other, just as the temptation has wrought. But a villainous affair it is, and will one day so blend and confound us all together, that no one shall be able to stand up and swear, "That his own great grand father was the man who did either this or that."
But we also find it in Emily Dickinson ("To Sue"):
Today is far from childhood,
But up and down the hills
I held her hand the tighter,
Which shortened all the miles.
And in W.H. Auden ("Plains")
… in brilliant moonlight, I have lost my way
And stood without a shadow at the dead centre
Of an abominable desolation,
Like Tarquin ravished by his post-coital sadness.
Which goes to show I've reason to be frightened
Not of plains, of course, but of me.
And W.S. Gilbert (The Grand Duke):
In the period Socratic every dining-room was Attic
(Which suggests an architecture of a topsy-turvy kind),
And Thomas Merton:
But (woe to us with dressed-up souls)
This demands deep study
Learning to unlearn,
Confinement in the freedom of that convent
Whose perpetual nuns (the poets say) are the stars
And flowers the Magdalens convinced for a day
But where, in the end, the stars are stars only
And flowers are flowers only
Which is why we call them
Stars and flowers.
Which is a good reason to follow Geoff Pullum's advice: "Don't put up with usage abuse". You may not care about summative which, but some day, they'll come for you.