3.1

4. Formal Fallacies 1

Fallacious arguments involve defective patterns of reasoning that preclude the premises from supporting the conclusion, even when those premises are true. You can further distinguish these defective patterns of reasoning by considering two distinct types of fallacies:

Formal fallacy:

A formal fallacy arises from a defect in the structure of a deductive argument such that these fallacies are evident simply from examining the argument's form, without regard to the specific content of the argument. Any argument having an invalid form contains a formal fallacy, so you can use methods you have learned for detecting invalidity (for example, the counterexample method) to determine whether an argument commits a formal fallacy.

Informal fallacy:

By contrast, an informal fallacy arises from mistaken presumptions about the content of an argument and can only be detected by examining the specific contentof the argument's statements.

Consider the following arguments, given along with their forms. Inspect both the content and form of each argument and determine whether it commits a formal fallacy. (Note: Only one argument form is given for each argument, even though a particular argument may in fact be a substitution instance for several forms.)

Argument A

P1:	All apples are fruits.
P2:	All oranges are fruits.
C:	All apples are oranges.

Form of Argument A

P1:	All A are F.
P2:	All O are F.
C:	All A are O.

Argument A a formal fallacy.

Argument B

P1:	Either this tree is an evergreen, or it is not a sequoia.
P2:	This tree is an evergreen.
C:	So, this tree is a sequoia.

Form of Argument B

P1:	Either E or not S.
P2:	E.
C:	S.

Argument B a formal fallacy.

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5. Formal Fallacies 2

Formal fallaciescan be identified by abstracting the form of an argument and evaluating it without regard to the specific content of the argument. Hence, if you are able to identify an argument's form, you should be able to determine whether the argument commits a formal fallacy. (Remember, you can determine an argument's form by replacing the content words with placeholder letters while leaving the connecting phrases alone. For example, a statement such as "If today is Monday, then tomorrow is Tuesday" could be represented as "If M, then T"where M stands for "today is Monday" and T stands for "tomorrow is Tuesday.")

Identify the correct form of each of the following arguments. (Note: Only one of the given argument forms is correct, even though a single argument may in fact be a substitution instance for several forms.) Then inspect both the content and form of each argument and determine whether it commits a formal fallacy.

Argument 1

P1:	If that building is the Empire State Building, then that building is a tall building.
P2:	That building is not a tall building.
C:	So, that building is not the Empire State Building.

Argument Form A

P1:	If E, then T.
P2:	Not E.
C:	Not T.

Argument Form B

P1:	If E, then T.
P2:	Not T.
C:	E.

Argument Form C

P1:	If E, then T.
P2:	Not T.
C:	Not E.

Argument 1is an instance of .

Argument 1 a formal fallacy.

Argument 2

P1:	Either this animal is a reptile, or else it is not a lizard.
P2:	This animal is a reptile.
C:	So, it is not the case that it is not a lizard.

Argument Form A

P1:	Either R or not L.
P2:	R.
C:	Not L.

Argument Form B

P1:	Either R or not L.
P2:	Not R.
C:	Not L.

Argument Form C

P1:	Either R or not L.
P2:	R.
C:	Not not L.

Argument 2is an instance of .

Argument 2 a formal fallacy.

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6. Recognizing Informal Fallacies

Whereas formal fallacies can be detected without regard to the specific content of an argument, informal fallaciesare a type of fallacy that can be detected onlyby examining the content of an argument's statements. This is because informal fallacies rely upon some mistaken presumption about the meaning, relevance, or implications of the specific content of the argument. Consequently, to detect such fallacies, you will need to have some knowledge of the key content words in the argument in order to adequately evaluate the meaning, relevance, and implications of the argument's statements.

Each set of three arguments includes oneargument that commits an informal fallacy. For each set, determine which one of the three arguments is fallacious.

Argument Set 1:

Argument A

P1:	Atomic particles move in a way that emits energy.
P2:	If an adequate amount of energy is emitted, then that energy produces visible light.
C:	Consequently, many things that are ultimately composed of atoms are visible to the naked eye.

Argument B

P1:	This table is not invisible to the naked eye.
P2:	But, ultimately, this table is composed of atoms.
C:	Evidently, atoms cannot be invisible to the naked eye.

Argument C

P1:	Most diurnal owls have yellow eyes.
P2:	The burrowing owl is diurnal.
C:	Most burrowing owls probably have yellow eyes.

Which of the three arguments from Argument Set 1 commits an informal fallacy?

Argument A

Argument B

Argument C

Argument Set 2:

Argument A

P1:	It is illegal to park in front of a fire hydrant.
P2:	Jack's car is parked in front of that fire hydrant, and a traffic officer has noticed it.
C:	Jack's car is likely to be towed or ticketed, or both.

Argument B

P1:	On its way to the emergency room, that ambulance sped through several red stoplights without stopping, and it was being followed by a police car.
P2:	It is against the law to speed through stoplights.
C:	It is safe to assume that the police officer in the car will issue a ticket to the ambulance driver once he catches up to her.

Argument C

P1:	A poll of 1,000 voters was taken in a town of 50,000 citizens.
P2:	Of the 1,000 voters polled, only 300 said they would vote to reelect the mayor, while 700 said they would vote for the challenger.
C:	The town will probably have a new mayor after the next election.

Which of the three arguments from Argument Set 2 commits an informal fallacy?

Argument A

Argument B

Argument C