3.1
7. Formal and Informal Fallacies – Practice
“Good” arguments (1) have all true premises, but they also (2) avoid fallacious reasoning. Thus, if you can detect either a false premise or a fallacy within an argument, then you know the argument is not a “good” argument (that is, a “sound” or “cogent” argument, for deductive and inductive arguments respectively). However, not all defective arguments commit a fallacy. Specifically, a fallacy is a defect in an argument that arises from faulty reasoning in the argument, not because the argument has one or more false premises. Furthermore, there are two distinct types of fallacies to look out for: informal and formal fallacies. A formal fallacy arises from a defect in the structure of an argument, so that you can identify these fallacies by simply examining the argument’s form, without regard to the specific content of the argument. By contrast, an informal fallacy arises from mistaken presumptions about the content of an argument and can only be detected by examining the specific content of the argument’s statements.
Determine whether each argument is a “good” argument or a defective argument. If it is defective, determine whether it also commits a fallacy, and indicate which type of fallacy (formal or informal) it commits.
Argument A
| P1: | Hawks and eagles are formally classified as belonging to the same family, Accipitridae. |
| P2: | In most cases, female eagles are considerably larger than male eagles. |
| C: | Female hawks are probably also larger than male hawks. |
Argument A a “good” argument; and it commit a fallacy.
Does Argument A commit an informal or a formal fallacy?
Argument A commits no fallacy.
Argument A commits an informal fallacy.
Argument A commits a formal fallacy.
Argument B
| P1: | On average, July is the warmest month of the year in Sweden. |
| P2: | Argentina borders Sweden. |
| C: | So, July is probably the warmest month of the year in Argentina, too. |
Argument B a “good” argument; and it commit a fallacy.
Does Argument B commit an informal or a formal fallacy?
Argument B commits no fallacy.
Argument B commits a formal fallacy.
Argument B commits an informal fallacy.
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8. True/False Review and Chapter Summary
Use your knowledge of formal and informal fallacies to determine which of the following statements are true. Check all that apply.
Some defective arguments are defective because they have one or more false premises, even though they do not commit a logical fallacy.
Informal fallacies never occur in deductive arguments.
If an inductive argument commits a fallacy, then you will be able to detect the fallacy only by inspecting the content of the argument.
All arguments that commit a formal fallacy are invalid arguments.
If an argument is inductive, it cannot commit a formal fallacy.
The term non sequitur is sometimes used to refer to fallacious reasoning.
Any argument with false premises is a fallacious argument.
Some informal fallacies occur in deductive arguments.
Fallacious arguments never have false premises.
Some fallacious deductive arguments are sound.
Some uncogent arguments neither contain false premises nor commit a fallacy.
If an argument is either unsound or uncogent, then it has one or more false premises or else it commits a fallacy.
All defective arguments commit a fallacy.
A formal fallacy can be detected without regard for the content words of the argument.
Fallacies that try to distract a listener from the rational implications of an argument by making pejorative claims about the argument’s author are formal fallacies.
