Why is it not correct to write, "The boy, who has a limp, was in an auto accident"?

Question

1.The boy who has a limp was in an auto accident. We do not know which boy is meant without further description; therefore, no commas are used.

2.The man, knowing it was late, hurried home. We used comma as the phrase/clause knowing it was late is not necessary to get the meaning of sentence. That means knowing it was late is not restrictive here.

My question is why the sentence #1 is not correct without the clause who has a limp although the sentences have the same categorised subject the man ** and **the boy in the first and second sentence respectively.

Why is it not correct to write by using comma The boy, who has a limp, was in an auto accident? and by not using comma The man knowing it was late hurried home? I'm confused about the defination of restrictive and non-restrictive here.

Answer 1

In sentence 1, "who has a limp" identifies the boy we are talking about in a group of other boys he may be in at the moment of speaking (identifying clause—no commas needed).

In sentence 2, "knowing it was late" is the Participle Clause, which should be surrounded by commas. The sentence might be written:

The man, who knew it was late, hurried home

(non-identifying clause; commas needed)—we know the man that hurried home.

If the sentence was

The man who knew it was late hurried home

it would mean that the other men he was with, didn't know it was late; otherwise, they too might hurry home.

Answer 2

Rompey is correct that 2 is a participle clause.

But 1 can be correct either way, but it depends on what you're expressing. Consider these examples:

My brother, who is married, won the lottery.

I have one brother. He is married. He won the lottery.

My brother who is married won the lottery.

I have multiple brothers, but only one of them is married. That specific brother has won the lottery.

In the second example, "who is married" is used to uniquely identify the brother I'm talking about. In the first example, "who is married" is tangential information which isn't used to identify the brother.

Therefore:

The boy who has a limp was in an auto accident.

We're focusing on not just any boy, but specifically the boy who has a limp. There are presumably boys who don't have a limp but we're not talking about them.

Answer 3

As per your first phrase, you need to think of the whole phrase "boy who has a limp" as the subject, rather than "boy" as the subject and "who as a limp" as additional information. This is why we don't need commas in the first phrase,* but do need commas in the second, since "man knowing it was late" can not be taken as the entire subject of the sentence.

Also, having a secondary phrase between two commas usually means it is not essential to the sentence (grammatically) and, more importantly, will make the sentence grammatically incorrect if removed. In the second phrase, removing the commas makes your sentence grammatically incorrect.

*I personally think adding commas in the first sentence is perfectly valid, and accurately depicts the cadence/way I would speak out the sentence. Not sure about the grammatical aspect of it, though.

Answer 4

I see no reason for the first sentence to be wrong.

Using commas to set apart the relative clause makes it a non-restrict relative clause, which suggests that it is not a necessary information about the subject. It would be wrong if the subject could not be identified through the context, in such a case, you could not really use commas to separate the relative clause since it is a necessary information that helps identify the subject, and necessary description about subjects can't be placed between commas. It is a rule.