5
Evidence
From your philosophy instructor, a request for evidence
for a claim is generally a request for an argument, or
for a better argument. While philosophers may from
time to time make use of scientific generalizations or
results, they generally avoid the messy and specialized
business of collecting and arguing about empirical data,
and confine their investigations to their armchairs. This
is a broad generalization; sometimes empirical evidence
from psychology, physics or other fields of inquiry can be
put to good use in philosophical arguments. But if you
do use such evidence from elsewhere, never just assume
that it solves your philosophical question: be careful to
explain exactly why it is relevant and exactly what we can
conclude from it, and do make sure that you accurately
report what the scientists have to tell us.
Philosophers still find a lot to argue about even when
they put empirical questions aside. For one thing, the
question of what sort of empirical evidence would be
needed to decide the answer to a question might itself be
a non-empirical question that philosophers discuss. For
another, philosophers spend a lot of time discussing how
different claims (which may be empirical) relate logically
to each other. For example, a common philosophical
project is to show how two or more views cannot be held
consistently with each other, or to show that although
two views are consistent with one another, they together
entail an implausible third claim. If successful, this type of
argument, known as a reductio ad absurdum or reductio for
short, shows that we have reason to reject at least one of
its premises.
EXAMPLE OF A REDUCTIO
s Premise 1: People sometimes ought morally to
do what they are not in fact going to do.
s Premise 2: If a person morally ought to do
something, then they could do what they ought to
do (Principle that “Ought implies can”).
s Premise 3: If a person is in fact going to do one
thing, then it is not the case that they could do
something else (Determinism).
s Conclusion (from 2 and 3): People never
ought morally to do what they are not in fact
going to do
Here, the conclusion contradicts the first premise.
If the argument is logically valid, it shows that the
three premises of the argument cannot all be true.
A further argument would be needed to show
which of the three premises ought to be rejected.
Philosophical arguments are not always in the form of a
reductio; we often need to start from some basic premises
that our ultimate conclusions will depend on. Unless they
are scientific results as mentioned above, they should
generally be claims that any reasonable reader can be
expected to agree with, and they might be drawn from
common experience, or from our stronger intuitions.
So, for example, one might begin an argument with the
intuition that murder is wrong if anything at all is wrong,
or with the common experience that things look smaller
when they are further away. When you introduce a set
of basic premises, you should be careful to avoid the
fallacy of begging the question – which is to say, using any
premises that one would reasonably doubt if not for one’s
prior acceptance of the conclusion the argument attempts
to establish. (This is the correct logical use of the phrase
“begs the question”, by the way. Avoid using the phrase
“begs the question” to mean raises the question, at least in
philosophy papers.)
EXAMPLE OF A QUESTION-
BEGGING ARG UMENT
s Premise (1): I have religious experiences.
s Premise (2): If anyone has religious experiences,
then God exists.
s Conclusion: God exists.
Note that in this argument, the term “religious
experiences” is ambiguous between two
readings. On one reading, it means genuine
experiences of something supernatural. On this
reading, premise (2) is plausible, but premise
(1) is question-begging, since one would have
to assume that God exists to think that one has
had a religious experience. On a second reading,
“religious experiences” means experiences as if
of something supernatural. But on this reading,
premise (2) is implausible. Finally, the argument
is not logically valid (it equivocates) if the term
“religious experiences” means a different thing
in each of the two premises. If the writer of this
argument had defined his terms more carefully,
its weakness would be clear. Ambiguous terms in
philosophical arguments are a common problem,
and can mask other weaknesses.
Since a lot of the things philosophers talk about are
very abstract, it may be difficult to bring our common
experiences and intuitions to bear on them. This is one
place where examples may be a useful source of evidence.
Examples can also help clarify the intended meaning of
terms. Philosophers make great use of hypothetical examples
in particular, and you should feel free to use them yourself.