Massimo Pigliucci has an interesting post at Scientia Salon on philosophical zombies. Massimo looks at David Chalmers’s argument for philosophical zombie arguments and, I think, does an excellent job at showing the problems with them. But in the discussion, a distinction is made that I find interesting.
Apparently, Chalmers admits that zombies are probably not naturally possible, but sees them as logically or metaphysically possible, and sees that as grounds for moving forward. Massimo spends some time looking at whether or not metaphysically possible and logically possible are the same thing. I’m not going to get into that, but if you find it interesting I definitely recommend his full post.
My interest is in the distinction between something being logically possible and it being possible given the natural laws of our universe. When I first read this distinction, I composed a long comment raising objections that such a distinction wasn’t, well, logical, then realized I was utterly wrong, and instead commented on the limitations of logic. Here’s the main portion of my comment as Scientia Salon:
I’m always a bit suspicious when people start talking about things being logically possible but not possible with our current natural laws, and yet proceed to try to make meaningful conclusions based on that logical possibility. Many things are logically possible given inaccurate premises. It’s logically possible for water to not be H2O, but only if my premises are wrong or incomplete or if I’m using an uncommon definition of “water”.
It’s not clear to me that even invoking the multiverse rescues this endeavor. We have no guarantee that logic as we understand it would have any traction outside of our universe. An assertion that logic necessarily transcends our universe strikes me as a statement of faith.
But this raises an interesting question. What exactly is logic? It turns out that logic is not one of those things that are easily definable. Per Wikipedia, here are some attempts at a definition:
Arranged in approximate chronological order.
The tool for distinguishing between the true and the false (Averroes).
The science of reasoning, teaching the way of investigating unknown truth in connection with a thesis (Robert Kilwardby).
The art whose function is to direct the reason lest it err in the manner of inferring or knowing (John Poinsot).
The art of conducting reason well in knowing things (Antoine Arnauld).
The right use of reason in the inquiry after truth (Isaac Watts).
The Science, as well as the Art, of reasoning (Richard Whately).
The science of the operations of the understanding which are subservient to the estimation of evidence (John Stuart Mill).
The science of the laws of discursive thought (James McCosh).
The science of the most general laws of truth (Gottlob Frege).
The science which directs the operations of the mind in the attainment of truth (George Hayward Joyce).
The analysis and appraisal of arguments (Harry J. Gensler).
The branch of philosophy concerned with analysing the patterns of reasoning by which a conclusion is drawn from a set of premisses (Collins English Dictionary)
The formal systematic study of the principles of valid inference and correct reasoning (Penguin Encyclopedia).
I’m not sure which of these I’d prefer. A distressing number refer to “reason” with most definitions of “reason” referring back to logic. But Gottlob Frege’s definition seems closest to my own current personal intuition about it, namely that logic represents the most fundamental relationships in our universe. These relationships are so fundamental, that we can take them and extrapolate truths using them, and often we’ll be right. (We won’t always be right. More on that in a bit.)
Does this mean that I think that, as Hilary Putnam discussed, logic is empirical? Yes and no. I think logic rests on foundations that are empirically observable. But it extends into realms that are not observable and often not physical. We extend it the same way we extend mathematics. (Indeed, everything I’m saying here can also be extended to include mathematics, which has often been called quantitative logic.) All logical reasoning could be called tautologies, although that is misleading because many tautologies are not intuitively obvious and many of them are important to understand.
But logic, even in its foundations, doesn’t feel empirical. I think the reason it doesn’t is because we didn’t learn it empirically. Remember that humans are not born blank slates. We come with cognitive machinery pre-wired to some degree. That pre-wiring includes an innate capacity for logical reasoning. (We don’t always use it, but we have the capacity.) Why do we have that capacity? Like anything else, we evolved it, almost certainly because it provided a survival advantage.
But that capacity evolved to deal with the working of the universe at the level at which we operate, on the scales well above quantum physics but much smaller than astronomical phenomena. Logic seems to work well at this in between scale, but there’s no guarantee that it will work at other scales. Although the results of astronomy and cosmology seem to show that it does seem to scale well to much larger scopes.
But when we go down to particle physics, logic takes a hit. Many things about how we logically expect the world to work start to be wrong. Of course, there are many interpretations that attempt to salvage some logic from observed quantum phenomena, but they are still forced to posit a world that would be considered illogical if experimental results didn’t force the issue. Indeed, some philosophers have even proposed an alternate system of logic based on quantum mechanics.
As I commented above, we also have no guarantee that logic would have any meaning outside of our universe. If there are indeed other universes in a multiverse with different natural laws, logic as we understand has a good chance of not working. (This incidentally is one reason why you have to treat logical arguments about the beginning of the universe with a large grain of salt. Extrapolating about the beginning of the universe based on how it works from within isn’t guaranteed to show anything.)
And, of course, even in settings where logic applies, logical reasoning is only as good as its premises. If our premises are wrong or incomplete, it doesn’t matter how good our logic is; we may still be completely wrong. (As an old programmer, I’m reminded of situations where I got the program logic perfect, but misunderstood some of the business requirements for the program I was writing; perfect logic but still wrong results.)
None of this is to say that logic isn’t tremendously useful. Reaching conclusions with logic (or mathematics) is far more likely to be correct than reaching them with intuition and emotion, at least on matters outside of everyday life. But we should be mindful of the limitations of reaching conclusions with logic alone. The history of science is one where logical extrapolation often pays off, but just as often doesn’t.
Think I’m wrong about this? If so, I’d love to read your…logic in the comments 🙂