When do you place a comma before a pronoun?

Question

My gut feeling often tells me to add a comma, but I'm not 100% sure. I'd like to know when you should and when you shouldn't use a comma. For example, does the following line requires a comma?

During my research, I discovered that Captain Hook was not able to fly.

Perhaps the sentence could be arranged differently, perhaps better. Since the time & location of the event could be hidden, I think a comma should be placed.

The comma placing in the above sentence is identical as the example given. But is the comma correct? When is and when is a comma out of order in cases when there is a pronoun halfway during the sentence?

_{Assuming I, he, she, we, etc. are pronouns. My native tongue is Dutch, so I'm not 100% sure what it's called in English.}

Answer 1

The comma is correct, but the sentence would also be acceptable without the comma.

In this case, the issue is that the subject is "halfway" through the sentence. It happens that the subject is a pronoun -- but the choice of whether to use a comma here does not depend on whether the subject is a pronoun.

Answer 2

Yes you need a comma because it is a passive sentence. Put the comma after the object. It doesnt matter how many words are contained in the object, although it gets awkward:

During my research into the fundamental physics of fictitious pirates, I discovered that Captain Hook was not able to fly.

In order to 'fix' it, change it from a passive to an active sentence.

I discovered that Captain Hook was not able to fly during my research into the fundamental physics of fictitious pirates.