Counter example

a counter example to a syllogism is a syllogism of the same form as the original, but with obviously true premises and false conclusion, in order to show the original to be invalid.

key point #1

the validity of syllogisms depends solely on their form. Certain forms are always valid; other forms are always invalid.

CAUTION

do not assume a syllogism is valid if you cannot think of a counter example to it. You may just need to be more creative.

key point #2

when developing counterexamples, try starting with a false conclusion, then find a middle term which results in true premises.

summary (something i'll try to include from now on)

an invalid argument may be exposed through the use of a counterexample. a counterexample is a syllogism of the same form as the original argument, but with obviously true premises and an obviously false conclusion.