Transcript PowerPoint No. 1a – A Little Logic

Basic Logic Definitions
Statement: A sentence that makes some
claim about the world.
True Statement: A statement in which the
claim does correspond to the way the
world actually is. (E. g.: The sky is
blue.)
False Statement: A statement in which
the claim does not correspond to the
way the world actually is. (E. g.: The
sky is pink.)
Argument: Group of statements in which
the truth of several (the premises) is
supposed to prove that another (the
conclusion) is true.
Proof: Proof exists when the premises’
being true gives you a good reason to
believe that the conclusion is true. For
example:
S. Wright is in Mr. Jones’ class.
Most of the students in Mr. Jones’ class
are boys.
Therefore, S. Wright is probably a boy.
An example of a lack of proof:
The director needs a singing, brown
haired actress for his play.
Most of the actresses at the audition are
brown haired.
Therefore, the director will probably find
the actress he needs for his play at the
audition.
What’s Needed for an
Argument to Be Good
• There must be a proof relationship
between the premises and the
conclusion.
• All the premises must actually be true.
Two Arguments
Most boys love to play sports.
Britney Spears is a boy.
Therefore, Britney Spears probably loves to
play sports.
Most popular singers have talent.
Britney Spears is a popular singer.
Therefore, Britney Spears probably has talent.
The first argument is bad.
The second argument is good.