In An Enquiry Concerning Human Understanding and A Treatise of Human Nature, David
Hume attempts to show us that inductive reasoning, and hence everything dependant
upon it (most notably science), is without a rational basis. Hume’s argument has come to
be known as the Problem of Induction.
The first step Hume takes in this argument is to divide all human knowledge into two
categories: matters of fact, and relations of ideas; the former being our sensory
observations which are not necessarily true of the idea in question, while the latter are
truths that are necessary by the idea’s essence. Already, a significant question should be
raised – can it be known that all knowledge falls into one of these two categories? If the
answer is no, then all of the arguments Hume presents are themselves based upon an
unknown premise; if the answer is yes, then explaining how is problematic. It clearly
cannot be verified as a matter of fact that this is true, and it is very problematic to explain
how it could be known as a relation of ideas. Thus, Hume’s division, though intuitive, in
fact appears to be self refuting.
Hume nonetheless goes on, and the next step in his argument is to look at the issue of
causation. Hume reasons that there can be no verification, through either matters of fact or
relations of ideas, that an event such as the bouncing of a ball is caused by the dropping
of said ball. All that can be verified is a continued conjunction, that there exists a
necessary connection has yet to be demonstrated. Hume here is opposing one of the
great ideas of the rationalists – the Principle of Sufficient Reason (PoSR). The PoSR is in
fact quite self explanatory, for every truth there must be a sufficient reason as to why it is
true. The PoSR therefore, can be used in response to Hume’s example, because when a
ball bounces there must be a sufficient reason (e.g. Gravity) as to why this is the case.
Hume might (and did!) attack the PoSR on the grounds that it cannot be justified either by
relations of ideas or matters of fact or relations of ideas, but to do so would be to ignore
one of the most fundamental principles since the time of Aristotle – the axiom. In order to
avoid reaching an eventually circular belief system, there are some things which must be
accepted simply on account of their self worth, and the PoSR appears to be one of these.
Although there is no widely agreed upon test for what should qualify something as an
axiom, beyond intuitiveness of course, there is nonetheless one criteria that is so weak
that no one can deny it – if it is psychologically impossible to deny it, then we should accept
it as an axiom. Once this criteria is set forth, it seems quite clear that the PoSR is such an
axiom, an opponent of the principle will usually give an argument against it, in other words,
they will try to give a sufficient reason to dismiss it. Furthermore, it seems impossible to
deny the principle, it is simply beyond the scope of the human mind to believe that things
can be true with a sufficient reason for its truth, and we presuppose the PoSR in our
everyday lives. Hume himself acknowledged that he did not believe his conclusions, but he
attributed this merely to an intuitive bias; of course, it was, at least on some level, intuitive
bias which had lead him to the division of all knowledge into matters of fact and relations of
ideas.
David Hume’s Problem of Induction is often cited as one of the great unsolved, and
unfathomable problems in philosophy, but challenging though it may at first seem, until the
objections outlined in this essay are given an adequate response, it seems that the mostproblematic characteristic of the Problem of Induction, is that so many people have spent
so much time trying to solve it.