|When a categorical syllogism that is invalid because both of its premises are negative.||No humans are birds. Some birds are not lawyers. Therefore some lawyers are not humans.|
|Also known as: two negative premisses|
Note that all the statements may be true individually, but the first two do not logically lead to the third.
Case Study One
“Since no Republicans are Democrats and some Democrats are not farmers, it follows that some farmers are not Republicans.” All of these statements appear sound, but the third does not logically follow from the first two.
Keep in mind that a fallacious argument does not entail an erroneous position.