The French philosopher René Descartes (1596-1650) set
himself the task of determining how certainty could be established. How could a
person be certain that their knowledge was set upon firm foundations? His
method was to doubt everything that could be doubted, with the idea that
anything that remained, and which could therefore not be doubted, must be
certain.
Descartes’ method of doubt
One aspect of this process of doubting was Descartes’s
conviction that all his beliefs must be jettisoned at the same time, as opposed
to considering each belief in turn as to whether or not it was open to doubt.
The process of looking at beliefs one at a time must only be done at the stage of
deciding whether or not they could be re-admitted to a person’s belief
portfolio because they were undoubted.
The analogy that Descartes used to illustrate his thinking
was that of a basket full of apples, some of which might be rotten. It was
outlined in his “Replies and Objections” that formed part of the second edition
of “Meditations on First Philosophy” (first published in 1642).
As is well known, the rot from one bad apple can easily
spread to its neighbours and it is therefore important to get rid of the bad
ones in order to preserve the health of the rest. If you suspect that not all
the apples are sound, the best move is not to look at each apple in turn but to
empty out the whole lot in one go and only return the good ones to the basket.
Descartes was of the view that beliefs could be treated just like apples; some
of them might be “rotten” and thus capable of infecting other beliefs, but the
only way of discovering them was to throw out the whole lot, good and bad, and
only replace the sound ones in the “basket” of beliefs that are certain.
Is this really such a good idea?
However, is this analogy a reasonable one? For one thing,
does it make sense to compare beliefs, which can be about anything, whether
serious or trivial, with apples that are identical to each other? For example,
how can “I believe that my cat has fleas” be treated in the same manner as “I
believe that God made all the little green apples”, when it comes to doubting
their certainty?
Also, what could be meant by one belief “infecting” another?
It would seem that Descartes was thinking about beliefs that are dependent on
other beliefs; for example “I believe that God will be my judge” is entirely
dependent on “I believe that God exists”. If the latter is thrown into doubt,
then the former cannot be held to be certain because it would have lost its
foundation. As Descartes would see things, these two beliefs cannot therefore
be considered separately.
However, the concept of doubting absolutely everything at
the same time is one that must lead to difficulties. For example, how can a
doubt be expressed if not by using language? But surely, in order to use
language, one must believe that the words one uses have particularly meanings.
That being so, to doubt everything would imply that one doubts the very
mechanism that one uses to do the doubting, which is clearly absurd. It has to
be concluded that Descartes’s scheme is open to serious objections.
The bad apple analogy is therefore an example of how
important it is to compare like with like when illustrating an argument, in
philosophy or anywhere else. Such analogies can often sound compelling when
first heard, but if there is too wide a divergence between the item under
discussion and the object to which it is being likened, then the argument is
likely to fall. In this case, it is unwise to assume that complicated things
such as beliefs can be treated in the same way as apples in a basket.
© John Welford
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