Proving a negative is, of course, impossible. That animals do not qualify as rational beings and, therefore, basic rights holders, is something we do not know from a syllogistic proof but from reflecting on the evidence and putting forth an explanation that makes better sense than any other. For example, no animal raises the question of whether animals are thinking beings, nor makes any TV programs on the subject. Animals, furthermore, have no central, crucial need of thinking, whereas without thinking human beings cannot begin to survive. Thinking for us is the mode of survival and flourishing -- we cannot count on our instincts to get on with our lives. Other animals, in contrast, can handle their lives by means of their instincts and for them their minimal abstract thinking is an aside, brought on usually by human beings, scientists who induce thinking in them while they are in captivity. From this we can conclude, sensibly, that it is valid to conclude that human beings are rational animal. That is what distinguishes us from other living things.
Let me just address very briefly the issue of whether machines can be rational? For example, what about Big Blue, IBM’s powerful chess machine, and the accompanying claims of the Artificial Intelligence community? This will be but a brief comment but needs to be included here to round out the discussion of whether animals, and perhaps other non-human beings, may have basic rights to life, liberty and property.
Machines are good at very rapid calculation, mainly because that is how human beings have designed them to be useful to them in various tasks. Even calculators are faster than most of us, when it comes to adding, subtracting, etc., not to mention figuring out the best strategy for winning at chess. Except for a few human beings, such as Gary Kasperov, who have devoted the bulk of their lives to it, most of us are pretty pedestrian about figuring out how to win at chess. So Big Blue isn't really big news.
What humans do that no machine, as we ordinarily understand them, can is to start thinking at will, on their own initiative. Human thinking, as we have repeatedly argued in this book, is self-generated, a matter of one's own free will, something machines aren't up to, plain and simple. That is why we can be mentally lazy but neither can animals nor machines. That is why when a machine misbehaves it makes no sense to blame it, anymore than it makes sense to blame or praise animals for their deeds. That is why believers in animal rights and artificial thinking machines do not address their arguments and appeals to non-human animals or powerful digital computers but, simply, to us. They know well enough that it is human beings who have the capacity to choose to think in certain ways and to stop thinking in others – to change their minds, in other words.
A thinking being is free to supervise its impulses, drives, and inclinations and is responsible for the outcome. This is what makes us unique and what puts us into the position of worrying about who and what we are, something other animals and machines, evidently, do not do. Whether this is wonderful or not isn't the issue here. All that needs to be noted that our humanity does leave us with certain unique attributes and it is pretty much pointless to constantly attempt to deny it.
Now when computers and non-human animals begin, all on their own initiative, to put on conferences about human intelligence, animal rights, or other controversial topics, when they start up laboratories and scholarly journals exploring these issues just as human beings do now, perhaps then we can begin to seriously consider that they have come to be pretty much like us and that our uniqueness in nature has disappeared.