Quote Originally Posted by it-ogo View Post
BTW if you are native English speaker, can you explain the situation with:
A woman, which I met.
A woman that I met.
A woman, whom I met.
The first sentence sounds odd to me. Generally we don't use "which" when the noun-antecedent is a human person -- only for animals or inanimate objects. And we don't use "who" for non-humans*. But "that" can be used with any antecedent -- human, animal, or inanimate. Thus, all of the following are okay:

A woman whom I saw. (but not "which")
A dog/table which I saw. (but not "whom")
A woman/dog/table that I saw.

When the antecedent is "woman," you can use either "whom" or "that", as far as the rules of grammar are concerned. Sometimes, there may be stylistic reasons to choose "who" instead of "that," but then it's a question of aesthetics, not grammar.

But it can get confusing if the antecedent is "dog" or "table" -- because in formal grammar, "that" is nearly always permissible, but "which" is sometimes incorrect. Mind you, even well-educated English speakers often ignore these traditional grammar rules, and use "which" and "that" interchangeably, because we can't remember when "which" is allowed and when "which" is not allowed. (If you want a more detailed explanation of when to use "which" and when to use "that," feel free to ask. But the short and simple answer is: When in doubt, use "that".)

* However, NB that the possessive whose can be used for humans and non-humans alike: "The planetoid Charon, whose surface is probably frozen methane..." is completely correct even in formal literary language.

P.S. Oops, I just thought of one example where my "when in doubt, use that" rule-of-thumb doesn't work -- when the antecedent is a proper noun, such as "John" or "Mrs. Smith" or "the HMS Titanic" or "Ukraine" or "my dog Spot," etc. In such constructions, "John" and "Mrs. Smith" and "Spot" would take who, while "Ukraine" and "Titanic" would take which:

"I have a dog named Spot, who loves to eat his own poop"
"I have a dog that loves to eat his own poop"