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Truth and Acceptability
When evaluating an argument internally, there are two
questions we ask:
- Are the premises true?
- Do the premises give support to
the conclusion?
Previously, we have covered the second question, and found
out that an argument can give strong or complete support to its conclusion even
if the premises aren't true. Of course, true premises are important for a good
argument also, so today we take a look at the first question.
Previously we defined truth as follows:
Truth is a property of statements. A statement is true if
the world actually is how the statement claims it is. It does not make sense to
call an argument true.
We are going to be looking at a more broad concept than
truth to start off with: acceptability. You may be wondering why they are
different concepts at all. Surely for a premise to be rationally acceptable all
it needs is to be true, right? This is a very plausible notion but the reality
is a little more complicated.
Logic itself does not deal with finding truth (that's what
we have other branches of epistemology for!), logic is concerned with preserving truth. What I mean by this is
that if we are given true premises, logic will show us what follows from them
and what doesn't, essentially preserving the truth of the premises until it
gets to the conclusion. We have been focusing on more practical techniques than
formal logic, so we need to find grounds for acceptability of premises too.
Sometimes we create arguments from premises we suspect or
know to be false, in order to investigate their consequences. This is one
example of how an acceptable premise may differ from a true one. Also, you may
be trying to convince someone of a particular conclusion but they do not agree
with one of your premises, although it may be true. Using this premise in order
to convince them would certainly not be acceptable, even though it may be true.
Remember, arguments are used for a purpose, and an argument that does not
fulfil its purpose because it uses true yet unacceptable premises can scarcely
be called a good argument.
So if acceptable premises are not simply true ones, what
makes a premise acceptable? The answer is not simple; there are a variety of
factors that come into play. In general terms, a premise is acceptable if it is
rationally believable. There have been many cases of widespread belief in
something that has turned out to be false (Earth at the centre of the universe
for example). These types of premises would be considered acceptable until
their error was uncovered. 'Common beliefs' is a phrase that captures this type
of thing well, although we must be careful to make sure that our arguments'
intended audience shares those beliefs. I could make a statement about
something well-known in Australian culture, and it may be an acceptable premise
here in Australia, but elsewhere it may not be. Premises can change between
being acceptable or not, but they cannot change between being true or not. It
may also be the case that two experts in a field are debating a point, and the
premises they are using are facts unknown to everyone outside their field.
These would also be acceptable because of the intended audience. Context is a
vital consideration in judgement of acceptability.
There is a problem with the above approach. If I were in a
debate with someone and they were telling me that the Earth was not flat, yet I
rejected this premise because I did not know it to be true, could it not be
argued that I ought to know that it is true? In these cases, a notion of
'widely held belief' is useful as there is a certain amount of belief that one
can be expected to have about certain topics, particularly if they are engaging
in arguments about the topic. You can probably see that these notions are not
particularly rigid or easy to define, but I hope you can see the types of
general conditions that we look for in acceptable premises.
There are of course other types of premises that we can deep
acceptable. Premises that are supported by a good sub-argument for instance
(which itself had acceptable premises) would be acceptable, whether that is
done in situ or somewhere else. When reading academic literature many premises
from other authors are used and the sources are detailed in the footnotes for
instance. Testimony from reliable sources could also be deemed acceptable,
providing that they are asserting something plausible and they are making
assertions in an area that does not go beyond the experience and competence of
the person who is making the claim. Claims that experts make about their field
of expertise are also acceptable premises. If a trained medical specialist
diagnoses us with something, then it can hardly be called rational to deny
their claim without any training in the area ourselves.
Another type of premise that we can deem acceptable is an
obvious a priori truth. An a priori
truth is one that we can know to be true without having to look at the world.
These are similar to necessary truths which we have talked about earlier, and
can be thought of as the same thing for our purposes. An example of an a priori truth is "kittens are
young cats". We do not need to find a kitten and find a cat and do a DNA
comparison to establish that kittens are indeed young cats; we know that the
statement is true because a young cat is the definition of kitten. This is in
contrast to a
posteriori truths, or contingent truths, which are truths that we
have to look at world to discover them rather than know them purely by
definition. An example of an a posteriori
truth is "kittens are cute". The same terms; a priori and a posteriori
can also apply to falsehoods with the same conditions.
Provisional premises are
statements you assume to be true so that you can see what the logical
consequences will be. You can do this even if you do not believe, or are
unsure, that the premises are actually true.
The judgement of premises as acceptable or not is a tough
process to formalize. I hope I have given you a decent overview of how
judgements should be carried out. Remember a few key guidelines..
- Premises are not acceptable if
your audience is not likely to believe them; unless
- The premise can be considered
'widely held belief', and it is a rational expectation that your audience should hold that belief.
- Obvious a priori truths are acceptable.
- Testimony from a reliable witness
and statements from experts are generally acceptable.
- Premises that beg the question,
regardless of their truth, are not acceptable.
- Premises may be accepted
provisionally to see what the consequences are.
When trying to convince someone of a conclusion, you must
start with premises that they accept. One specific type of unacceptable premise
was introduced very briefly in a previous article: begging the question.
Begging the question is when you assume the conclusion of an argument in its
premises. Premises that do this are unacceptable even if the audience agrees
that they are true, because it means the argument is not actually proving
anything at all. This is actually a very common problem and will be covered in
more detail in future articles.
Premises that are unacceptable are simply those that do not
fit the criteria, but I will cover a few more specifics. Claims that are easily
refutable are obviously not acceptable. For instance, if someone were to make a
general claim and there were obvious counter-examples, that claim would not be
an acceptable premise. Claims that are a
priori false are not acceptable, and neither are premises that are not
consistent with each other within an argument. Vague or ambiguous premises can
also be rejected, even if they are true, because argument often relies on the
details, and making mistakes about the details of something due to a vague or
ambiguous statement is something to be avoided. Highly controversial premises
may also not be acceptable, or at least require further support to become
acceptable.