Muriel: I admire Favilla’s novels, but she does not deserve to be considered great writer.
Muriel's 1st Claim
I admire Favilla's novels. does John say he doesn't admire them?
No, he makes no reference to Favilla at all.
Muriel's 2nd Claim
Favilla does not deserve to be considered a great writer. does John say she should be considered great?
No, he makes no reference to Favilla at all.
Muriel's 3rd Claim
Her style is distinctive does John say it isn't distinctive?
No, he makes no reference to Favilla at all.
Muriel's 4th Claim
Her subject matter is not varied enough. does John say it is varied enough?
No, he makes no reference to Favilla at all.
Evaluate
Since John didn't disagree with any of Muriel's explicit claims (and since John isn't talking about Favilla at all), we can tell that John must be objecting to something more implied or assumed.
In fact, John explicitly says that he's objecting to the "criterion" that Muriel is using.
She is saying, .
He says, .
Goal
Let's look for something like, whether or not diversity in subject matter is a necessary criterion for considering someone is a great writer.