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Philosophy 103: Introduction to Logic
Test: The Structure of Arguments

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Part I. Arguments (30 points). Indicate whether the passages below are arguments or non-arguments. If the passage is an argument, tell whether it is inductive or deductive and diagram it using the numbers provided..

A. [1] Since I studied hard for this logic test, and [2] since I understand the material very well, [3] I will probably make a good grade.

Inductive Argument:  The word "probably" in the conclusion is a strong clue.  The argument is inductive since the conclusion does not follow with logical necessity.  I could study hard and understand the material but not make a good grade for other reasons--e.g., distractions, illness, excused absence.

B. [1] There is probably gold in Abbeville County [2] because there are many abandoned gold mines there and [3] Ransom’s geology guide lists sites in this county as places to look for gold. 

Inductive Argument.  The word "probably" is again a clue here.  It's possible, albeit unlikely, that all the gold has already been mined and none is left.  The claim is not supported with absolute certainty.

C. [1] If students were environmentally aware, they would object to the endangering of any species of animal. [2] But the well known Greenwood white squirrel is endangered [3] as it has completely disappeared from the Lander Campus [4] because the construction of the Learning Center and new Science Complex has destroyed its native habitat. [5] Yet, no Lander student objected. [6] Therefore, Lander students are not environmentally aware.

Inductive Argument.  The conclusion only follows with probability.  Nevertheless, note that the concluding part of this argument is deductive--in particular, the passage contains an argument of the type called modus tollens:  "If p then q, not-q; therefore not-p."  Statement 4 does not logically entail statement 3, and statement 3 does not logically entail statement 2.

Image: Statement 4 is claimed as a reason of statement 3 which is claimed as a reason for statements 1,2, and 5 which in turn are claimed as reasons for statement 6.

D. [1] In 60 out of 90 attacks in the dark, catfish strike guppies along the guppy's meandering path. [2] Consequently, catfish can track the chemical trails in guppy-wakes in the dark.

Inductive Argument.  The conclusion only follows with probability.  The catfish might use some other means to track the guppies (e.g., electric fields sensors or a combination of methods).

E. [1] God is good [2] because by definition God cannot be evil or indifferent.

Deductive argument.  The conclusion follows by the conventional definition of the term "good."

Image: Statement 2 is given as a reason for statement 1.

F. [1] I was late for class [2] because my car ran out of gas and [3] I could not find a gas station.

This passage is an explanation.  A causal connection is offered, not an argument to prove I was late.


Part II. Truth, Validity, and Soundness (20 points). Write in the blanks below the word "true" or the word "false" in accordance with the truth or falsity of the statement.

1. ______False_____ All deductive arguments with true premisses are always valid.

2. ______True______ All sound deductive arguments are valid.

3. ______False_____ All valid arguments have true premisses and a true conclusion.

4. ______True______ All deductive arguments with true premisses and a false conclusion are invalid.

5. ______True______ Some invalid arguments have true premisses and a true conclusion.

6. ______False_____ All valid deductive arguments are sound.

7. ______False_____ All deductive arguments are valid.

8. ______False_____ All deductive arguments with a false conclusion are invalid.

9. ______True______ All arguments with a false statement in them are unsound.

10. _____True______ All sound arguments are valid and have all true statements in them.

Part III. Premiss and Conclusion Indicators (20 points). Place a check mark in the appropriate column for the following words.





1. since
2. for
3. thus
4. therefore
5. because
6. yet
7. moreover
8. as
9. hence
10. accordingly


Part IV. Short Answer (30 points). Explain the meaning of the following terms and give an example of each. 

A. statement: 

A verbal expression which has a truth value.  "Many trees are green."

B. sentence which is not a statement:  

A nonstatement does not have a truth value. "Is this test any fun to take?"

C. deductive argument:  

An argument which claims the conclusion follows with necessity. "John is James' brother, so James is John's brother."

D. inductive argument: 

An argument whose conclusion follows with probability.  "Mary is 78 years old, so she cannot climb Mt. Everest."

Optional-Extra Credit
(5 pts.): Diagram the structure of the following complex argument.

(1) Bacteria responsible for the familiar infectious diseases are becoming ever more resistant to antibiotics. (2) Certain strains of enterococci bacteria no longer respond to vancomycin. (3) Vancomycin was thought to be the drug of last resort that could beat any bacterial infection. (4) In the race for supremacy, microbes are sprinting ahead.

Image: Statements 2 and 3 are claimed to be reasons for statement 3 which, in turn, is claimed to be a reason for statment 4.

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