Seeing how diverse and fluid English grammar is, it’s hard to draw up precise, firm rules. What’s wrong with that sentence? Factually, nothing: at times it’s very hard indeed. But grammatically, maybe? Still nothing, in my view. But some pedants would not agree. And they have a point.
Their point, which they see as a rule, is that any present participle, the form of the verb ending in -ing — seeing or talking, for instance — must have a noun (or pronoun) as its subject, to show who or what is doing the seeing or talking or whatever. So look at this sentence: playing poker, it’s essential to bluff. Here the pedants would ask, and I tend to agree with them, just who is playing poker? I don’t say, as they would, that the sentence is flatly wrong. But personally I’d write if you’re playing poker, or for anyone playing poker.
The pedants have a further point. Try this: watching the blonde on the bicycle, Bond’s Ferrari slammed into the parked taxi. There’s the subject of watching, the noun Bond’s Ferrari; the grammar is fine. But alas, the sense is absurd: it was James Bond who took his eyes off the road, not his car. Use a subject, the pedants say, but also — and here they’re wholly right — be sure it’s the right one: the driver, not the Ferrari, in this case.
All this is good advice. But a firm, universal rule it is not. Wisely or not, English has come to allow certain present participles to stand on their own. Seeing, in my opening sentence above, is one: plainly the it in that sentence isn’t the subject of seeing. In fact there’s no subject, and none is needed. But suppose the sentence ran seeing he’s clever at finance, you should accept his advice. Ah, we might say, here we’ve got you to show who’s seeing. But in reality not so: the speaker is using seeing as a stand-alone, he doesn’t care who exactly can see the financier’s cleverness.
Depending is another such stand-alone: we’ll go by bus or train, depending which is cheaper. And the list of such words or phrases is steadily expanding, often to pedants’ dismay, sometimes to mine. There’s another problem with this ‘rule’. Many words in -ing are in effect nouns: dreaming comes naturally, running is soon learned, swimming takes real skill. But what about stirring chutney is tedious? Sure, you can always translate such a phrase into the stirring of chutney. But as the phrase stands (and it’s perfectly good English), this stirring is plainly part of a verb — the present participle, you might reasonably think — whose object is chutney. Yet it needs no noun, even by the most pedantic standards. Grammarians can answer that point; they’d call this stirring a ‘gerund’ (no, don’t ask), not a participle at all. But that does leave the ‘rule’ looking a trifle threadbare, doesn’t it?
There are also many words in -ing that double as adjectives: his manners were winning, his words charming, his temper worrying, its consequences alarming. Here I’d agree with the grammarians: these may have begun life as the present participles of verbs, but when used like this they are indeed adjectives, so the ‘rule’ simply doesn’t apply to them and isn’t meant to.
But at that point I’d ask, what are rules for? They’re thought up by experts to govern or at least guide the inexpert rest of us, who may know little and care less about what is a participle, what a gerund and what an adjective. Must we learn all that before we apply the rules? And then, even when we’ve done so, and on top have learned where the rules are meant to apply and where not, we find there are umpteen exceptions, such as the stand-alone words I’ve mentioned! I’d call that the sort of ‘rule’ we’d be better off without.
I don’t mean we simply shouldn’t bother; the pedants’ advice is, by and large, well worth taking note of. But advice it is, not a rule, let alone a precise or firm one. Like the (better-founded) ‘rule’ against splitting infinitives, it deserves attention, but not supine obedience.