In an article in the Scientific American (here) Shermer points to ‘consilience of inductions’ or ‘convergence of evidence’. This is a principle that I have held for many, many years. Observations, theories and explanations are only trustworthy when they stop being a string of a few ‘facts’ and become a tissue or fabric of a great many independent ‘facts’.
I find it hard to take purely deductive arguments seriously – they are like rope bridges across a gap. They depend on every link in the argument and more importantly on the mooring points at either end. A causeway across the same gap does not depend on any single rock – it is dependable.
There is one theory that is put forward often and, to many, is ‘proven’, that is that brains can be duplicated with a computer. The reasoning goes something like: all computers are Turin machines, any program on a Turin machine can be duplicated on any other Turin machine, brains are computers and therefore Turin machines and can be duplicated on other computers. I see this as a very thin linear string of steps.
Step one is a somewhat circular argument in that being a Turin machine seems to be the definition of a ‘proper’ computer and so yes, all of those computers are Turin machines. What if there are other machines that do something that resembles computing but that are not Turin machines? Step two is pretty solid – unless someone disproves it which is unlikely but possible. The unlikely does happen; for example, someone did question the obvious ‘parallel lines do not meet’ to give us non-Euclidian geometry. Step three is the problem. Is the brain a computer in the sense of a Turin machine? People have said things like, “Well, brains do compute things so they are computers.” But no one has shown that any machine that can do any particular computation by any means is a Turin machine.
No one can say exactly how the brain does its thinking. But there are good reasons to question whether the brain does things step-wise using algorithms. In many ways the brain resembles an analog machine using massively parallel processing. The usual answer is that any processing method can be simulated on a digital algorithmic machine. There is a difference between duplication and simulation. No one says that a Turin machine can duplicate any other machine via a simulation. In fact, it is probable that this is not possible.
This is the sort of argument, a deductive one, that is hardly worth making. We will get somewhere with induction. It takes time: many experimental studies, methods have to be developed, models created and tested etc. But in the end it will be believable – we can trust that understanding because it is the product of a web or fabric of dependent inductions.