The Building Blocks of Logic
SYLLOGISMS
IT’S A LITTLE BIT LIKE MATH…
IF A=B
 And C=A
 Then B=C

All humans have brains.
Mrs. Miedwig is a human.
Mrs. Miedwig has a brain.
SOUND, VALID, OR INVALID?

Sound= The premises are both unequivocally
true

Valid= At least one of the premises is up for
debate

Invalid= The two premises do not have to lead
to that conclusion
RELATIONSHIP TO TOULMIN
Warrant: All humans have a heart.
Data/ Support: Mrs. Miedwig is human.
Claim: Mrs. Miedwig has a heart.
Let’s talk about ORDER:
Warrant: Good schools contain strong fine arts
programs.
Data/ Support: Crystal Lake South has a strong fine
arts program.
Claim: Crystal Lake South is a good school.
ENTHYMEME

A syllogism as stated in writing, typically with one
premise missing. This usually means there’s more to say
to defend your ideas.

Examples:

Assisted suicide is wrong because killing is wrong.

If killing babies is wrong, then abortion is obviously wrong.

Capital punishment is wrong because it is killing someone.
ANOTHER EXAMPLE

Full syllogism –
 All
humans are mortal. (This one is left out of the
enthymeme)
 Michael is human.
 Therefore, Michael is mortal.

Enthymeme – Michael is mortal because he’s
human.
EXAMPLE IN MLK

“Since I feel that you are men of genuine good
will and that your criticisms are sincerely set
forth, I want to try to answer your statement in
what I hope will be patient and reasonable
terms.”
Syllogism:
Sincere criticism from good people should be answered.
You are good people with sincere criticism.
Your criticism should be answered.
ANOTHER EXAMPLE

“The purpose of our direct-action program is to
create a situation so crisis-packed that it will
inevitably open the door to negotiation.”
Syllogism:
Situations that are crisis packed open the door to
negotiation.
The situation we are creating is crisis packed.
Our situation will open the door to negotiation
PRACTICAL APPLICATION

Look for assumptions in your own writing and
be sure to defend them. (Warrants!)

Look for assumptions in other people’s writing
and attack them. (Debates!)

Watch out for invalid syllogisms/ invalid logic.
 Example:
Men are stronger than women, so women
cannot serve in the military.
“THE CASE FOR TORTURE”

Find examples where Levin uses syllogisms
within his argument and write them out.

Write a syllogism for Levin’s OVERALL
argument.

Is Levin’s argument sound? valid? invalid?
Explain your answer.