A few weeks ago, the official Twitter account for the forthcoming movie Deadpool tweeted, “A love for which is worth killing.” Name developer Nancy Friedman commented, “There are some slogans up with which I will not put.” Obviously, with a name like Arrant Pedantry, I couldn’t let that slogan pass by without comment.
— Deadpool Movie (@deadpoolmovie) January 12, 2016
The slogan is obviously attempting to follow the old rule against stranding prepositions. Prepositions usually come before their complements, but there are several constructions in English in which they’re commonly stranded, or left at the end without their complements. Preposition stranding is especially common in speech and informal writing, whereas preposition fronting (or keeping the preposition with its complement) is more typical of a very formal style. For example, you’d probably say Who did you give it to? when talking to a friend, but in a very formal situation, you might move that preposition up to the front: To whom did you give it?
This rule has been criticized and debunked countless times, but even if you believe firmly in it, you should recognize that there are some constructions where you can’t follow it. That is, following the rule sometimes produces sentences that are stylistically bad if not flat-out ungrammatical. The following constructions all require preposition stranding:
- Relative clauses introduced by that. The relative pronoun that cannot come after a preposition, which is one reason why some linguists argue that it’s really a conjunction (a form of the complementizer that) and not a true pronoun. You can’t say There aren’t any of that I know—you have to use which instead or leave the preposition at the end—There aren’t any that I know of.
- Relative clauses introduced with an omitted relative. As with the above example, the preposition in There aren’t any I know of can’t be fronted. There isn’t even anything to put it in front of, because the relative pronoun is gone. This should probably be considered a subset of the first item, because the most straightforward analysis is that relative that is omissible while other relatives aren’t. (This is another reason why some consider it not a true pronoun but rather a form of the complementizer that—that is often omissible.)
- The fused relative construction. When you use what, whatever, or whoever as a relative pronoun, as in the U2 song “I Still Haven’t Found What I’m Looking For”, the preposition must come at the end. Strangely, Reader’s Digest once declared that the correct version would be “I Still Haven’t Found for What I’m Looking”. But this is ungrammatical, because “what” cannot serve as the object of “for”. For the fronted version to work, you have to reword it to break up the fused relative: “I Still Haven’t Found That for Which I’m Looking”.
- A subordinate interrogative clause functioning as the complement of a preposition. The Cambridge Grammar of the English Language gives the example We can’t agree on which grant we should apply for. The fronted form We can’t agree on for which grant we should apply sounds stilted and awkward at best.
- Passive clauses where the subject has been promoted from an object of a preposition. In Her apartment was broken into, there’s no way to reword the sentence to avoid the stranded preposition, because there’s nothing to put the preposition in front of. The only option is to turn it back into an active clause: Someone broke into her apartment.
- Hollow non-finite clauses. A non-finite clause is one that uses an infinitive or participial form rather than a tensed verb, so it has no overt subject. A hollow non-finite clause is also missing some other element that can be recovered from context. In That book is too valuable to part with, for example, the hollow non-finite clause is to part with. With is missing a complement, which makes it hollow, though we can recover its complement from context: that book. Sometimes you can flip a hollow non-finite clause around and insert the dummy subject it to put the complement back in its place. It’s too valuable to part with that book doesn’t really work, though It’s worth killing for a love is at least grammatical. It’s worth killing for this love is better, but in this case A love worth killing for is still stylistically preferable. But the important thing to note is that since the complement of the preposition is missing, there’s nowhere to move the preposition to. It has to remain stranded.
And that’s where the Deadpool tweet goes off the rails. Rather than leave the preposition stranded, they invent a place for it by inserting the completely unnecessary relative pronoun which. But A love for which worth killing sounds like caveman talk, so they stuck in the similarly unnecessary is: A love for which is worth killing. They’ve turned the non-finite clause into a finite one, but now it’s missing a subject. They could have fixed that by inserting a dummy it, as in A love for which it is worth killing, but they didn’t. The result is a completely ungrammatical mess, but one that sounds just sophisticated enough, thanks to its convoluted syntax, that it might fool some people into thinking it’s some sort of highfalutin form. It’s not.
Instead, it’s some sort of hideous freak, the product of an experiment conducted by people who didn’t fully understand what they were doing, just like Deadpool himself. Unlike Deadpool, though, this sentence doesn’t have any superhuman healing powers. If you ever find yourself writing something like this, do the merciful thing and put it out of its misery.