Unit 3 Flashcards
What is a deductive argument?
Deductive are the arguments that claim to establish the truth of their conclusions conclusively.
What is a nondeductive argument?
Those that claim to offer good but not conclusive reason for believing their conclusions.
When is a deductive argument valid?
If the conclusion follows from the premises
All cats are mammals.
All dogs are mammals.
Therefore, all cats or dogs.
Is this a valid argument?
No it is not. The conclusion does not follow from the premises.
All cats have brown fur.
Jackie is a cat.
Jackie has brown fur.
Is this a valid argument?
It is.
The conclusion follows from the premises.
Can an argument have true premises and true conclusion but be invalid?
Provide example.
Yes that is possible. Example: Cats are a feline. Dogs are canine. Therefore, dogs are animals.
What are 5 ways of casting doubt on premises?
- Counterexample for a universal statement.
- Breaking if-then connection.
- Pointing out doubtful implications of the premises.
- Casting doubt on scientific statements
- Raise doubts about the reliability of sources.
When is a deductive argument sound?
For the deductive argument to be sound it must be valid and all of it’s premises must be true.
What is counterexample method of showing that the conclusion does not follow from the arguments?
In this method you provide another argument that follows the same pattern but makes the obviously false conclusion.
For example someone argues:
(1) All good teachers respect students.
(2) All who respect students listen to what they say.
(C) All who listen to students are good teachers.
The pattern here is
(1) All P1s are P2s
(2) All P2s are P3s
(C) All P3s are P1s
Your counterexample could be
(1) All cats are mammals
(2) All mammals are animals
(C) All animals are cats.
Obviously a false conclusion from the true premises
What are three methods of showing that deductive argument is invalid?
- Counterexample method.
- The possible situation method.
- Matching the argument to the known valid/invalid argument forms.
What is the “possible situation method” of proving that the conclusion does not follow from the arguments.
In this method you provide the explanation of the situation which would make the conclusion not follow from the premises. For example:
(1) All goods athletes have good coordination
(2) John has good coordination
(C) John is a good athlete.
You provide the explanation: “John may have good coordination but it is possible that he is very slow and has never engaged in organized sports activities. So it is possible that John is not a good athlete.”
What is the method “matching the argument to the known valid/invalid argument forms”?
In this method you discover the argument’s form first then match that form to one of the known valid/invalid argument forms.
What are 2 limitations of “matching the argument to a known valid/invalid form”?
- The argument in question must be in form of one of those known valid/invalid forms.
- Those known valid/invalid argument forms are not a widespread knowledge and not everyone knows about them.
What is a systematic study of methods for proving whether the deductive argument is valid/invalid on the basis of their form called?
Formal Logic.
What are 4 steps of writing a critical comment?
- Summarize the argument’s premises and conclusion.
- State whether the argument is valid - the conclusion follows from the premises.
- If the premises are arguable, try to cast doubt on them.
- See if slight changes can be made to improve the argument. (Principle of Charitable Interpretation.)
