One syllogism that is often used in this class has the following form:
P1 If A Then B P2 Affirm A C Conclude B
P1 If a person has blue eyes, then they have red teeth. P2 I have blue eyes. C I have red teeth.
When an argument is in this syllogistic form the premises will always lead to the conclusion, but the truthfulness of the premises will still be undetermined from an analysis of the argument form.
Arguments can also be shown to be bad if they don't properly use the form (by affirming B instead of A, for instance).