FlyingWhaleThat's right. If a modifier seems to be modifying a certain part and that's what makes most sense, then there's no reason to say it's unclear. In general, we don't want to look for
technical ambiguity ("it's possible to read this more than one way"); rather, we want to address
real ambiguity (the intent is genuinely unclear) or mismatched terms (e.g. a noun modifier attaching to a verb, or an "it" pronoun whose only possible antecedent is plural). Consider this sentence:
My parents didn't want any donuts, and my siblings were stuffed from a day spent watching movies and devouring candy bars, so I ate them all.Here, "them" is nowhere near "donuts," and there are plenty of intervening plural nouns, but do we have any doubt what I ate? Does anyone read this and think that I ate my family, or some movies, or the candy bars that were already eaten? No! Sure, the GMAT might be nice and say "so I ate the donuts myself," but if we saw "them," we wouldn't instantly need to fix it, because the ambiguity is only technical.
As for infinitives, it's hard to make any firm rules, since there are so many ways to use infinitives and other verb forms. In the case at hand, we're looking at something fairly specific: the construction "verb + infinitive" ("want to go," "try to do something," "continue to read," "learn to code," "plan to arrive early," "fail to appear," "agree to perform," "decline to state"). What do these have in common? The infinitive verb describes an action we want to refer to--something we wanted or tried to do, or something we did not do. In those cases, the infinitive is at the very least clearer than an -ing, in part because -ing forms have so many different uses. In many cases, the infinitive is the only option--you can't say "plan arriving early" or "I want going." Of course, there are many exceptions. An extremely common form in spoken English is "keep + -ing." We say "keep reading," but we could never say "keep to read." (The same goes for "stop" and "quit"): "stop bothering me," "quit smoking." So as you see, it's hard to say that infinitives are generally preferred, but in cases where they do work, an -ing form may be less clear.
Also note that the usage in the last paragraph is different from another very common "verb + infinitive" case, in which we use the infinitive to show the purpose or effect of an action: "dress to impress," "exercise to live longer," "say something to offend you." In those cases, the -ing form doesn't work at all, since that form does not show purpose. "I exercise living longer" doesn't really have any meaning.
So while there are plenty of uses for -ing forms (present participles, gerunds, etc.), there are definitely constructions in which they don't work well.
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