Obviously Lee commits a logical fallacy here.
One being correct depending on whether your opponent in a debate is CAPABLE of making a logical argument is utter nonsense.
That would be like me saying to a 5-year old (and yes, in this case i am comparing myself to a 5-year old):
Pink elephants are real and if you (the 5-year old) cannot make a logical argument for the opposite, then I assume I must be right.
Explanation:
Let's suppose that the 5-year old cannot make a logical argument to counter my premise, and can only go by the fact that he has never seen a pink elephant, and knows (as opposed to atheists) that you cannot make an absolute statement in the negative (such as: "there is no God in the entire universe") without having omniscient knowledge, does that mean I am right?
Of course not.
Lee being right is not dependant on the skills of his opponent in a debate, but it depends on what the truth is. Now I there might still BE a logical counter argument, even if I am unable to make it! But here it goes...
Anyway, to answer the question:
Yes, Lee. Begat can mean "have a son", or have a "grandson" or "have a great grandson" etc.
So when Adam begat Seth, he had a ......son (with the .... being either blank, grand-, great grand-, etc).
I have admitted this and we have all agreed on that.
However, what you did, is that you introduced a different meaning (and think you could slip it by me unnoticed).
You added the words "ancestor of" that as far as I know is not in the text.
So your text then becomes:
When Adam begat Seth, he had a ......son (with the .... being either blank, grand-, great grand-, etc) who was an ancestor of Seth.
This is adding text, and if that is allowed, we are not going anywhere anytime soon.
The verb "to beget" means to have a descendant, but it does NOT mean "to have a descendant, who is an ancestor of".
So sorry Lee, but try again. You have certainly been creative in trying to answer that burning question, but you have used means that you will have to prove is allowed by the Hebrew. I think you won't be able to. But I admire your attempt.