In his most recent contribution to the debate, Ball says that my argument consists of nothing more than
a demand for anyone who disputes its conclusion to refute it. He concludes that people who do not agree with the
conclusion do not have any reason to accept it.

However, it is obviously not the case that my argument consists of nothing more than such a demand. My argument
involves an appeal to the formal principle of justice. It also assumes that our intuition that it would not be
morally permissible to use unconsenting brain-damaged humans in harmful scientific research is correct. The 
challenge is to identify a morally relevant difference between the case involving the brain-damaged humans and
the nonhuman animals. This is a perfectly legitimate move. Moves like this are made all the time in ethical
argument, and no-one seriously disputes the legitimacy of such moves. It is a form of ethical argument that comes
up all the time.

Another example of such a move would be this. Someone living in the nineteenth century might be trying to
challenge the view that it is morally permissible to enslave people with dark-coloured skin. He might say "Well,
you wouldn't think it morally permissible to enslave people with light-coloured skin, would you? What exactly is
the morally relevant difference?" Ball has contended that the argument against slavery was fundamentally different
to this, but there is no evidence that he has any grounds for this contention other than that it seems quite 
important for his argument to succeed. Since the falsity of this contention would cast Ball's argument into
serious doubt, it's his burden to defend it. He should cite the literature that was written about the issue of
slavery at the time and demonstrate that fundamentally different arguments were used. I have not checked myself.
I would imagine that a common reply to this line of argument back then would have been that morally relevant
differences could be found, that black people were in some way inferior and less deserving of moral consideration.
I would imagine that that would have been the focus of the debate. We shall see, if Ball ever gets around to
meeting his obligation to investigate the matter. But the point would still remain that essentially the same form
of argument is being used. If it's legitimate in this case, we need to explain why it's not legitimate when
arguing about the status of nonhuman animals.

To summarize: ethical arguments which appeal to the formal principle of justice do not beg the question. If that
were so, we would hardly be able to get anywhere in ethics.