The September/October edition of Philosophy Now has four more letters with interesting objections to my article ‘The Zombie Threat to a Science of Mind’ in the May/June edition (reprinted on this blog). I respond to these objections below.

Bill Meacham, USA

Bill argues that talk of zombies is meaningless. Most philosophers who argue for the incoherence of zombies adopt a behaviourist analysis of mental concepts: if to be in pain is just to behave in a pained way, then the notion of a zombie (something that behaves in a pained way but does not feel pain) is as incoherent as the notion of a married bachelor. I raised problems with this approach in my article.

However, rather than taking the behaviourist route, Bill instead adopts a verficationalist conception of linguistic meaning: ‘By definition, this zombie is an exact physical duplicate of a conscious human, and there is no possible way for anyone to distinguish this zombie from a human being as they both act exactly the same.’  Verificationalism about meaning, the view that a sentence has meaning if and only if its truth can be empirically verified, was popular in the first half of the twentieth century amongst the Vienna Circle. However, it is now almost universally rejected. One difficulty is that the view seems to be self-undermining: the statement ‘A sentence is meaningless unless it can be verified’ cannot itself be verified, and is therefore meaningless by its own lights.

Russell Berg, Manchester

Russell is interested in what distinguishes a good philosophical thought experiment from a bad one. He outlines an intriguing and original view as to what we might reasonably expect from a good thought experiment. Russell suggests that if we are to imagine certain entities in a thought experiment, the thought experiment must outline a ‘Rational Development Path’ (RPD) which explains how, in the scenario being envisaged, those entities came to exist:

‘To illustrate, let’s imagine a person who instead of eating food, for energy plugs herself into the electricity supply every night whilst sleeping. A viable RDP for this electric person is that her ancestors had a stomach to digest food, but this was replaced by genetically modified cells which could store electricity and which could safely transfer current from a grid system.’

Russell goes onto suggest there is no plausible RDP for zombies, on the grounds that humans could not have evolved without consciousness:

‘…our metabolism relies on the cooking of food; but for this to occur requires imagination, which is an attribute of consciousness, thus lacking from the philosophical zombie twin. Further, for language to develop there needs to be creativity, which would also be lacking from a zombie devoid of consciousness.’

The conclusion is that the zombie thought experiment doesn’t pass the test for a reasonable thought experiment, and so ought to be rejected.

I would like to make two responses.

Firstly, natural selection is ultimately interested in behaviour. It doesn’t matter for survival whether you really do have imagination or creativity, but whether you behave as though you have imagination and creativity. There is a perfectly coherent scenario in which there are complex mechanisms that are set up to behave just like imaginative and creative people, even though they lack the conscious experience we associate with these states; such creatures would survive just as well as real world humans. Perhaps Russel has an argument that such mechanisms are incoherent, but to just assume that they are incoherent in this context is to beg the question (in the proper sense of this term meaning assuming what you’re trying to prove rather than the currently popular corruption where the phrase is used to mean raises the question).

Secondly, I think that the requirements we set for a given thought experiment should depend on what we want the thought experiment for. In the context of the zombie argument, we are interested in what is coherent, in whether a given scenario involves contradiction. Given this focus, a scenario in which zombies come into existence by a fortuitous arrangement of particles would do the job. Of course such a scenario is highly improbable, but the question is not whether it is likely but whether it is coherent.

Kristine Kerr, from The Internet

Kristine argues that thinking about zombies is pointless as zombies don’t actually exist. I argue at some length in the article that sometimes what’s possible has implications for what’s actual, due to the logic of identity. Given that Kristine does not engage this argument, it’s difficult to know how to respond other than by pointing out that I do outline an argument for this in the article.

Kristine finds it significant that the philosophy department in the university where she studied was replaced by a business school. Perhaps this is symptomatic of contemporary priorities; but the question of whether or not those priorities are good ones is surely what we should be concerned with.

Dave Darby, Tooting, London

Dave states that the notion of human brain processes without consciousness is no more coherent than the notion of two sets of puckered lips meeting without a kiss. It’s a lovely analogy, but it is important to note that puckered lips meeting without a kiss is an uncontroversial example of incoherence. In contrast, there is a debate concerning the coherence of zombies, with intelligent views on either side. Even those who deny the coherence of zombies see the force of the intuition that such creatures are readily imaginable, and go to great lengths to try to undermine that intuition. I think Dave owes us an argument to the conclusion that zombies are like the meeting of lips without a kiss (i.e. incoherent), rather than like flying pigs (i.e. coherent).