Having established this interpretation of these words, Hume goes on to
ask: What can be the ground in reason for the principle universally
adopted, that the law of cause and effect rules phenomena, and that a
cause which has been followed by an effect once will be followed by the
same effect always? And he concludes that no rational ground can be
found at all, that it is the mere result of custom without anything
rational behind it. We are accustomed to see it so, and what we have
been so perpetually accustomed to see we believe that we shall continue
to see. But why what has always been hitherto should always be
hereafter, no reason whatever can be given. The logical conclusion
obviously is to discredit all human faculties and to land us in
universal scepticism.

It was at this point that Kant took up the question, avowedly in
consequence of Hume's reasoning. He considered that Hume had been misled
by turning his attention to Physics, and that his own good sense would
have saved him from his conclusion had he thought rather of Mathematics.
Kant's solution of the problem, based mainly on the reality of
Mathematics, and especially of Geometry, is the direct opposite of
Hume's.

It will be most easy to give a clear account of Kant's solution by using
a very familiar illustration. There is a well-known common toy called a
Kaleidoscope, in which bits of coloured glass placed at one end are seen
through a small round hole at the other. The bits of glass are not
arranged in any order whatever, and by shaking the instrument may be
rearranged again and again indefinitely and still without any order
whatever. But however they may be arranged in themselves they always
form, as seen from the other end, a symmetrical pattern. The pattern
indeed varies with every shake of the instrument and consequent