"Dangling participles" abound in written English. They may occur when we write a sentence with two clauses: an introductory clause, and an independent clause. The first one modifies the second one, that is, the first clause gives information that helps us understand the second clause. The introductory clause has a participle but no subject, so this participle will automatically refer to the subject of the independent clause. For example:
"Having finished my breakfast, I put on my coat and left the house."
According to Strunk and White, the rule is that "a participial phrase at the beginning of a sentence must refer to the grammatical subject." As is the case with grammar rules in general, this one aims to eliminate ambiguity so that the sentence is as clear as possible. Why do dangling participles create ambiguity?
Strunk and White offer a great example:
"Being in a dilapidated condition, I was able to buy the house very cheap."
Since the subject of the independent clause is "I," the participial phrase automatically refers to that pronoun. It would seem as if the speaker had been in a dilapidated condition. To make it right, the subject of the independent clause should be the house. How would you change the sentence then?
"Despite rushing to catch it, the bus left without him."
It wasn't the bus that was rushing, was it? What would be the correct way to phrase this sentence?
Yet this rule is not violated if the introductory clause is an absolute construction. We will talk about absolute constructions next time.
Reference: Strunk, William and E.B. White. The Elements of Style