Wesley C. Salmon,
THE SCOPE OF LOGIC
When people make statements, they may offer evidence to support them or they may not. A statement that is
supported by evidence is the conclusion of an argument, and logic provides tools for the analysis of arguments.
Logical analysis is concerned with the relationship between a conclusion and the evidence given to support it.
When people reason, they make inferences. These inferences can be transformed into arguments, and the tools of
logic can then be applied to the resulting arguments. In this way, the inferences from which they originate can be
Logic deals with arguments and inferences. One of its main purposes is to provide methods for distinguishing those
which are logically correct from those which are not.
In one of his celebrated adventures, Sherlock Holmes comes into possession of an old felt hat. Although Holmes is
not acquainted with the owner of the hat, he tells Dr. Watson many things about the man -- among them, that he is
highly intellectual. This assertion, as it stands, is unsupported. Holmes may have evidence for his statement, but so
far he has not given it.
Dr. Watson, as usual, fails to see any basis for Holmes's statement, so he asks for substantiation. "For answer
Holmes clapped the hat upon his head. It came right over the forehead and settled upon the bridge of his nose. 'It is a
question of cubic capacity,' said he; 'a man with so large a brain must have something in it.' "
Now, the statement
that the owner of the hat is highly intellectual is no longer an unsupported assertion. Holmes has given the evidence,
so his statement is supported. It is the conclusion of an argument.
We shall regard assertions as unsupported unless evidence is actually
to support them, whether or not anyone
evidence for them. There is a straightforward reason for making the distinction in this way. Logic is concerned
with arguments. An argument consists of more than just a statement; it consists of a conclusion along with
supporting evidence. Until the evidence is given, we do not have an argument to examine. It does not matter who
gives the evidence. If Watson had cited the size of the hat as evidence for Holmes's conclusion, we would have had
an argument to examine. If we, as readers of the story, had been able to cite this evidence, again, there would have
been an argument to examine. But by itself, the statement that the owner is highly intellectual is an unsupported
assertion. We cannot evaluate an argument unless the evidence, which is an indispensable part of the argument, is
To distinguish assertions for which no evidence is given from conclusions of arguments is not to condemn them.
The purpose is only to make clear the circumstances in which logic is applicable and those in which it is not. If a