How can I translate the supplementive phrase?

Question

John, knowing that his wife was expecting a baby, started to take a course on baby care. = John, who knew that his wife was expecting a baby, started to take a course on baby care.

As I know,'knowing that his wife was expecting a baby'is supplementive phrase for John. In Comprehensive Grammar of the English Language, 'knowing that his wife was expecting a baby' also means'who knew that his wife was expecting'.

With this theory, I wonder if I'm right about sen tenses below.

1. Julia, being a nun, spent much of her life in prayer and meditation. = Julia, who was a nun, spent much of her life in prayer and meditation.

2. Julia, wearing a hat, looks beautiful. = Julia who wears a heat, looks beautiful.

Answer 1

Yes, your sentences are correct. The second versions include relative clauses, while the first versions include present participle phrases that are sometimes called "reduced relative clauses". Nevertheless, there are some caveats:

1) The present participle form is non-finite, so it lacks tense. The reader, therefore, must infer when the action occurs, usually by taking cues from other parts of the sentence (finite verbs, adverbials, etc.). It doesn't make much difference in your sentences, because the tenses are consistent. ("Was expecting" and "started" are both in the past tense; "was" and "spent" are both in the past tense; "wears" and "looks" are both in the present tense.) However, consider the following:

Julia, being a nun, has spent much of her life in prayer and meditation.
Julia, who will be a nun, has spent much of her life in prayer and meditation.

A reader of the first sentence will assume that the action of "being" takes place at the same time as the action of "has spent". However, the second sentence places the first action in the future. Therefore, these two sentences are not equivalent.

2) Although the second version of sentence 2 ("Julia, who wears a hat, . . ."¹) is a correct transformation of the first version, most English speakers would use the progressive aspect ("is wearing") instead.

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¹ I added a comma and fixed the spelling of "hat".

Answer 2

There is a very subtle difference in meaning.

John, who knew that his wife was expecting a baby, started to take a course on baby care.

He knew about the baby, but maybe that's unrelated: perhaps he took it because he wanted to take it, anyway.

Knowing that his wife was expecting a baby, John started to take a course on baby care.

(I have re-shaped the sentence to make it more natural, but...) This is maybe the same as the above. But it really has a different "feeling" to an English speaker. There is a sort of implicit 'because'. BECAUSE he knew about the baby, he did this... It's not 100% necessary, but there's a strong feeling in that direction.

The easiest way to show the "unrelated" form in English would be something like: "John, who HAPPENED TO KNOW..." (by coincidence)

The same applies to your Julia nun examples. Or does it?

• Julia, wearing a hat, looks beautiful. (she's ugly hatless)
• Julia, who wears a hat, looks beautiful. (she's pretty anyway, and I'm telling you about the hat in unrelated news)

For the hat stuff: look up "restrictive clause" and "unrestrictive clause", which will help your grammar.