only experimental results that actually do refute a theory – and not just any theory, it must have been a genuine contender in a rational controversy – constitute ‘corroboration’.

The fact that it is not a real engine is irrelevant to the argument against solipsism. After all, not everything that is real has to be easy to identify.

In this respect the discovery of other universes is quite reminiscent of the discovery of other planets by early astronomers.

If one does not accept a proposed explanation of a set of observations, making the observations over and over again is seldom the remedy. Still less can it help us to create a satisfactory explanation when we cannot think of one at all.

is there a single virtual-reality generator, buildable once and for all, that could be programmed to render any environment that the human mind is capable of experiencing?

Any image generator is a rudimentary sort of virtual-reality generator, but the term ‘virtual reality’ is usually reserved for cases where there is both a wide coverage of the user’s sensory range, and a substantial element of interaction (‘kicking back’) between the user and the simulated entities.

one can criticize this narrow notion of universality because it classifies a task as being in a computer’s repertoire regardless of the physical resources that the computer would expend in performing the task.

Far from denying free will, far from placing human values in a context where they are trivial and insignificant, far from being pessimistic, it is a fundamentally optimistic world-view that places human minds at the centre of the physical universe, and explanation and understanding at the centre of human purposes.

The study of logic itself revealed that the scope of logical deduction as a means of discovering the truth is severely limited.