What is an existential fallacy?

Question

Does it have something to do with method acting?

Answer 1

All unicorns are animals, therefore some animals are unicorns.

Answer 2

Definition:

An existential fallacy is a formal logical fallacy which is committed when a categorical syllogism employs two universal premises to arrive at a particular conclusion. Because it is a formal fallacy, such a categorical syllogism is invalid. The form of this syllogism is:

All P are Q.

All X are P.

Therefore, some X are Q.

The two premises are universal (All...) whereas the conclusion is particular (Some...). In some cases, it may seem like such an argument should be valid. For example:

All mammals are animals.

All cats are mammals.

Therefore, some cats are animals.

Part of the problem here is that all cats are mammals, not some. But the real error lies in the fact that the class of X above may be a class without any members. For example:

All spirits are supernatural beings.

All gods are spirits.

Therefore, some gods are supernatural.

If the category "gods" has no members, then the above syllogism cannot establish the truth of the claim that some gods are supernatural. In a categorical syllogism, if the two premises are universal, then the conclusion must also be universal.