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Researchers suspect that early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system, helping it to attack only harmful things.

I'm really confused about these.

  1. What is the subject of "helping"? If one thing is right, why are the others not? I cannot refute the ideas myself.
    a) early exposure to pets carrying bacteria on their fur
    b) early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system(the whole of the previous clause, if this is the subject we can rephrase the sentence as follows: "~ immune system, and this(or it) helps it to attack only harmful things")
    c) the proper functioning of the immune system

  2. What does "it" after "helping" indicate? Is it "the immune system"? Am I right?

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  • The matrix clause includes the subordinate clause, so it cannot be the subject of the sub clause. Without having any technical knowledge of the topic, we can probably conclude that the understood subject is "early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system", or perhaps just "the proper functioning of the immune system". Yes: "it" refers to "the immune system"
    – BillJ
    Jan 1, 2021 at 7:31
  • Thank you BillJ. In this case, you mean the whole matrix clause(early exposure ~ immune system) is not the implied subject of -ing clause? Then, "The proper functioning of the immune system helps the immune system to attack only harmful things" is right? isn't this awkward but natural?
    – Mcreaper
    Jan 1, 2021 at 7:31
  • The idea that the whole matrix clause can be an implied subject of -ing clause is not mine. It is from the Comprehensive Grammar of the English Language. Please refer to the book.
    – Mcreaper
    Jan 1, 2021 at 7:34
  • I don't use that book. It's often the case that there is no syntactic determination of the understood subject, so the subject has to be determined by inference. Looking at it again, I'd say the salient interpretation is probably "the proper functioning of the immune system", but we'd need an expert on the topic of immune systems to be 100% certain.
    – BillJ
    Jan 1, 2021 at 7:42

2 Answers 2

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Quick Answer: The subject of "helping" is "exposure," or if you want the full noun phrase, the subject is "early exposure to pets carrying bacteria on their fur." The subject does not include "may encourage the proper..." because that is the beginning of the predicate (verb + object of the verb) of the sentence. The antecedent of "it" is "the immune system."

Long Answer: This may be easier to explain using a simpler example to start:

Consider the following two sentences: (1) The gymnast performed well. (2) The gymnast impressed all of the judges.

These two sentences have the same subject: the gymnast. If we combine these two sentences into one sentence, we don't have to include the subject twice because that would sound repetitive:

(1) + (2) combined: The gymnast performed well and impressed all of the judges.

In this combined sentence, the gymnast did two things: She performed well, and she impressed all of the judges. The subject of the verb "performed" is "the gymnast," and since there is no other subject listed before the second verb, it is understood that the subject of the verb "impressed" is also "the gymnast."

This combined sentence above is grammatically correct, but there is another way of expressing the same idea. The second sentence can be expressed as a participle phrase that is added to the first sentence.

Note: A participle phrase is a present participle and its predicate. A present participle is the "-ing" form of a verb that is functioning as a verb. (If the -ing form of a verb is functioning as a noun, as in "Swimming is fun," then it is called a gerund instead of a present participle.)

If we combine the two sentences using a participle phrase, we omit the subject of the second sentence (omit second occurrence of "the gymnast") and convert the second predicate ("impressed all of the judges") to a participle phrase ("impressing all of the judges):

(1) The gymnast performed well (2) The gymnast impressed all of the judges --> impressing all of the judges

(1) + (2) combined: The gymnast performed well, impressing all of the judges.

A present participle of a verb does not have a tense, so the sentence can be in the past tense, future tense, or any other tense, but the participle will always have the -ing form. (Side note: The infinitive is another verb form that has no tense.)

The participle phrase can appear before or after the subject of the sentence. It can even appear in the middle of the sentence. It is understood that the subject of the sentence also functions as the subject of any participle phrases added to that sentence, regardless of whether the participle phrase appears before or after the subject.

Examples of different locations of a participle phrase:

(1) Hoping he would not be recognized, Mr. Smith wore a disguise to the event. (2) Mr. Smith, hoping he would not be recognized, wore a disguise to the event. (3) Mr. Smith wore a disguise to the event, hoping he would not be recognized.

In all three examples, "Mr. Smith" is the subject of the sentence. Therefore, in all three sentences, "Mr. Smith" is the subject of "wore" as well as the subject of the participle phrase "hoping he would not be recognized."

Let's apply this to the OP's question:

OP's example: "Researchers suspect that early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system, helping it to attack only harmful things."

This sentence can be broken down into two sentences:

(1) Researchers suspect that early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system (2) Researchers suspect that early exposure to pets carrying bacteria on their fur may help the immune system to attack only harmful things.

The author combined those two ideas into one sentence by converting the second sentence into a participle phrase: The subject can be omitted the second time and the verb is converted to its "-ing" form. Additionally, to avoid repetitiveness, the second occurrence of "the immune system" is replaced with the pronoun "it":

(1) + (2) combined: Researchers suspect that early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system, helping it to attack only harmful things.

Remember that the subject of the main verb in a sentence also functions as the subject of a participle phrase in that sentence. So the subject of "helping" is "exposure." The antecedent of "it" is "the immune system," since early exposure to pets helps the immune system to attack only harmful things.

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  • Hi, welcome to ELL Stack Exchange. Great answer!
    – Eddie Kal
    Jan 1, 2021 at 4:23
  • Thank you for the detailed answer. But as far as I know, the whole of the matrix clause can be a subject of -ing clauses according to the Comprehensive Grammar of the English Language page 1122. On the page, the book says in the sentence "the siren sounded, indicating that the air raid was over", a subject is "the siren sounded". So, I always consider this option. Even if you consider this, the answer is the same?
    – Mcreaper
    Jan 1, 2021 at 7:11
  • I'm not familiar with that book. You have to keep in mind that the English language does not have a single authority on issues of grammar, style, and usage, and you will sometimes come across established, reputable sources that contradict each other. If you have reason to follow the rules in that book, then follow those rules. In my mind, though, a sentence cannot function as a subject of a verb. Rather, the subject of that sentence can serve as the subject of another verb, in the case of a participle phrase. I would say that the subject of "indicating" is "the siren."
    – zunojeef
    Jan 1, 2021 at 17:50
  • Based on my knowledge of immunology, it makes the most sense if the subject of "helping" is "early exposure..." The sentence is clarifying "the proper functioning of the immune system" as "to attack only harmful things." It is saying that early exposure to pets encourages proper functioning of the immune system, which is to say that early exposure helps the immune system to attack only harmful things. It doesn't make sense to say proper functioning of the immune system helps it to attack only harmful things, since attacking only harmful things is a precondition for proper immune function.
    – zunojeef
    Jan 1, 2021 at 18:14
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    @Mcreaper In a case like this, you can't draw a conclusion purely based on syntax without considering the semantics. In other words, you have to understand what the sentence means and what each part means in order to determine the subject of "helping". The subject is most definitely not the entire clause. I agree with this answer that it is "exposure".
    – Eddie Kal
    Jan 2, 2021 at 2:20
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helping is a present/active participle, and it heads the participial clause "helping it to attack only harmful things".

The British Council grammar page about participial clauses offers several situations where you can use a participial clause. One is to give the result of an action.

The bomb exploded, destroying the building.

Generally, the subject of the main clause is also the subject of the participial clause. The subject of the main clause is the part before the verb:

early exposure to pets carrying bacteria on their fur

The object of the participial clause is it, which refers to the immune system.

You can check whether your interpretation is correct by converting the participle to simple present and then pugging in the subject and object that you have identified. You can then check that it is grammatically correct and makes sense:

early exposure to pets carrying bacteria on their fur helps the immune system to attack only harmful things.

If you plug in the wrong bits, it doesn't make sense- in this case because the sentence now contains two verbs:

early exposure to pets carrying bacteria on their fur may encourage the proper functioning of the immune system helps the immune system to attack only harmful things.

... and this one is a tautology

the proper functioning of the immune system helps the immune system to attack only harmful things.

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