How do you know if a claim is true?
There are many ways arguments can go wrong, but only a
few ways to make them logical. Logical arguments provide convincing
evidence for claims. What kind of evidence counts depends on what
kind of claim has been made.
Opinions are never false, because the evidence
is in the mind of whoever is giving the opinion. For example:
I don't like to eat green vegetables.
Is that true or false? To find out, you'd have to be
inside the body of the person who said it. Since that's impossible,
there is no reason to question it. Of course, opinions don't count
for much when someone is trying to persuade you. You can always answer,
"I have a different opinion."
To decide if the evidence is convincing, you first have
to know what sort of claim has been made. Claims come in at least
An empirical claim makes a statement about the
world. For example:
The moon is made of green cheese.
We need scientific knowledge about the world to test an empirical
claim. Scientific knowledge is public information gained by careful
observations and experiments. We have lots of evidence that the moon
is made of rock, including the close-up observations of astronauts, so
we know that the green-cheese claim is false.
An analytical claim makes a statement about the
meaning of words or other symbols. For example:
The Constitution gives us freedom of speech.
We need knowledge about words and symbols to test an analytical
claim. We might consult a document and use a dictionary or other
reference to find out how people have agreed to interpret a word.
In this case, the claim is true because free speech is guaranteed in the
First Amendment to the Constitution.
A valuative claim makes a statement about what
is good or bad, right or wrong. For example:
People should read books instead of watching so
To test a valuative claim, we appeal to standards of value.
In this case, the standard might be the value of literacy. Valuative
claims often carry assumptions about empirical claims not directly stated.
Here, we are assuming that reading books makes us more literate than watching
TV, which according to scientific studies of vocabulary growth, is also
true. Answering valuative claims requires us to decide which value
standard is higher. In this case, we might argue that literacy is
a higher standard than relaxation or pleasure.
A metaphysical claim makes a statement about our
very existence. For example:
All men are created equal.
To test a metaphysical claim, we appeal to revelation, that
is, to statements of faith. Reconciling conflicting metaphysical
claims usually requires that we appeal to a common revelation. For
example, if we understand that the introduction to the Declaration of Independence
expresses an essential truth about our existence on earth, then it is true
that all men are created equal. But if someone disputes the authority
of the Declaration, we might not be able to resolve the question of whether
all people are equal or not. We may have to agree to disagree, because
our opponent does not share our faith.
When we've stripped down an argument to the bare essentials--when
it's stated in neutral, unemotional language, it's free of opinions, and
we are willing to grant the authority and impartiality of the speaker--then
our final questions are:
This is how we get at the truth, the whole truth, and nothing
but the truth.
1. What kind of claim is being made?
2. What evidence supports that claim?
here to see some examples and try your hand at evaluating the truth of
here to find out about some popular fallacies, or ways arguments go wrong.
here to return to the quotes from Nothing But the Truth.