] The point is that only the heir (ie the hypothetical son) could do this, since he would be the person who was giving up some rights. Even if this son did not agree, then, unless he was singularly undutiful, he would provide for his sisters and mother.

I don't believe that JA's words contradict this, do they? And I certainly didn't mean to imply otherwise either.

I was responding to your statement:

"No, not breaking the entail, but continuing it. Mr Bennet's estate was entailed on the male line. His son would have inherited it after his death, and would then, he presumes, looked after the female Bennets."

JA made it clear that Mr Bennet had intended to "join [with his son] in cutting off the entail -- NOT just in providing for the females out of the income from the estate.