MODR 1770 Lecture Notes - Deductive Reasoning

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silverminnow879

21 Oct 2012

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The point of devising an argument is to try to show that a statement, or claim, is worthy of acceptance. The point of evaluating an argument is to see whether this task has been successful whether the argument shows that the statement (the conclusion) really is worthy of acceptance. Inductive is intended to provide probable not conclusive support for its conclusion. Deductive is intended to provide logically conclusive support for its conclusion. A deductive argument that succeeds in providing such decisive logical support is said to be valid; a deductive argument that fails to provide such support is said to be invalid. Because of the guarantee of truth in the conclusion, deductively valid arguments are said to be truth-preserving. A deductively valid argument that has true premises is said to be sound. A sound argument is a good argument that gives you good reasons for accepting its conclusion.

Related Questions

1. Consider the following argument: All fish can swim. You are a fish. Therefore, you can swim. Which of the following best describes this argument?

A. It is valid but unsound.

B. It is valid and sound.

C. It is invalid and unsound.

D. It is inductively weak.

2. In a valid deductive argument: (circle the correct answer)

A. the premises must all be true.

B. it is impossible for the premises to be true and the conclusion false.

C. the premises must be false if the conclusion is false.

D. it is impossible for the premises and the conclusion to be false together.

sangriagoose906

For example, consider the following argument:
"Measles can't be cured by antibiotics, since Measles is caused by a virus, and antibiotics can't cure a viral infection."

We can see that the argument contains the word "since," which is a premise indicator. We know that what follows "since" will be the premises. We also know, through the process of elimination, that what precedes the word "since" is the conclusion. So my standardized argument will look like this:

1) Measles is caused by a virus. 2) Antibiotics can't cure a viral infection. therefore, 3) Measles can't be cured by antibiotics.

Now we can see the relationship of support between the premises and conclusion. We are asked to accept the conclusion, "Measles can't be cured by antibiotics," based on the two supporting premises. Notice that all of the premises and the conclusion are statements, that is, complete sentences that are either true or false. Also, notice that the premise indicator "since" has been omitted. We always omit premises and conclusion indicators when putting arguments into standard form and make sure that the components of our argument are statements, that is, complete sentences that are either true or false.

For credit on this assignment, do the following:

1) Put the following arguments into standard form:

a) "All dogs are carnivores, consequently, Max is a carnivore, for the reason that Max is a dog."

b) "Rebecca does not pray at the mosque, for she is not a Muslim and only Muslims pray at the mosque."

c) "To every existing thing God wills some good. Hence, since to love any thing is nothing else than to will good to that thing, it is manifest that God loves everything that exists."

2) Create your own argument:

a) Construct an argument of your own using two different premise indicators and one conclusion indicator with the following conclusion: "Now, more than ever, everyone needs to take a class in logic."

b) Then put the argument into standard form.

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MODR 1770 Lecture Notes - Deductive Reasoning

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