A colleague asked about a sentence similar to the following:
Implementing personnel policies is the only real delegation left to make, which requires involvement at all executive levels.
Let us accept, for the sake of argument, that the “which” clause is a nonrestrictive clause – i.e., that the comma belongs there (otherwise, take out the comma, replace which with that, and you have a coherent sentence – but one that implies that there may also be tasks left to undertake that don’t require involvement at all executive levels). The problem, then, is that it’s not clear what the which refers to.
Normally, for a nonrestrictive clause, the referent of the “which” comes right before the comma (when it doesn’t, we call it a dangler); for instance, in “The only real delegation left to make is implementing personnel policies, which require…” the “which” refers to “personnel policies.” It is also possible for which to refer to the entire gerund construction, made clear by using a singular verb: “The only real delegation left to make is implementing personnel policies, which requires…”
So one might think that it should read OK here, with “which requires” referring to the nearest singular noun, “the only real delegation,” but it’s separated from the comma by the infinitive “to make,” and that makes a mess of it. Compare “He gave it to the dog, which was hungry” with “He gave it to the dog to eat, which was hungry.” We want to attach the “which” to the infinitive, which is not possible. And so the reader is confused and then, looking for a place to attach it, and having to cast around in the sentence at large, isn’t sure whether it refers to delegation, implementing, or the overall state indicated by the first clause (as in “The dogs are falling into the flowers, which is causing a mess”).
So pick what the which refers to and rephrase it accordingly with the referent as close to the which as possible, as per the examples above. If the referent is in fact delegation, the phrasing requires at least a little recasting: “Implementing personnel policies is the only real delegation left to make, a delegation which requires involvement at all executive levels.”