Logic - chap. 1 - arguments

Logic; chapter 1 - slide 1

Logic - chap. 1 - arguments

What is logic? The study of the principles used to

distinguish between good and bad arguments.

Clarifications Logic is not the study of the

reasoning process Logic is not primarily concerned

with establishing the truth or falsity of statements.

Logic; chapter 1 - slide 2

Logic - chap. 1 - arguments

Why are arguments important? A way to resolve disagreements

peacefully Part of the process of finding the

truth For conceptual questions,

arguments may be the principal method of determining truth

Central to our humanness

Logic; chapter 1 - slide 3

Logic - chap. 1 - arguments

The notion of an argument A set of statements of which one or

more are put forward as reasons for accepting another statement as true.

Logic; chapter 1 - slide 4

Logic - chap. 1 - arguments

An example of a simple argument If we interfere with the publication of false

and harmful doctrines, we shall be guilty of suppressing the liberties of others, whereas if we do not interfere with the publication of such doctrines, we run the risk of losing our own liberties. We must interfere or not interfere with the publication of false and harmful doctrines. Hence we must either be guilty of suppressing the liberties of others or else run the risk of losing our own liberties.

Logic; chapter 1 - slide 5

Logic - chap. 1 - arguments

Distinguishing between arguments & non-arguments Examples

Logic; chapter 1 - slide 6

Logic - chap. 1 - arguments

I don’t think it would be a good idea to take the American Revolution course this term, because it conflicts with a course I need for my major, and my schedule would have more balance if I took a science course instead.

Nearly half the homes in the country subscribe to cable TV. Basic cable service usually includes local TV channels, such as the four networks, and one or more channels. For an additional fee, subscribers can also receive movie channels and other specialized programs

Logic; chapter 1 - slide 7

Logic - chap. 1 - arguments

Analyzing arguments 3 steps (1) Identify & distinguish between

premises & conclusion(s) Clues

premises & conclusion may occur in any order

Logic; chapter 1 - slide 8

Logic - chap. 1 - arguments

Example: No coal tar derivatives are nourishing foods, because all artificial dyes are coal tar derivatives, and no artificial dyes are nourishing foods.

look for indicator words don’t let flourishes &

repetitions confuse you

Logic; chapter 1 - slide 9

Logic - chap. 1 - arguments

Example: In the twentieth century, physicalism has flourished. But the after-image is not in physical space. The brain-process is. So the after-image is not a brain-process. (J.J.C. Smart, “Sensations and Brain Processes,” Philosophical Review, April 1959)

Logic; chapter 1 - slide 10

Logic - chap. 1 - arguments

missing Ps & Cs do not make an argument invalid (or weak) Example: Mary attended

the opera; so her lamb must have attended the opera too.

several arguments may be strung together

Logic; chapter 1 - slide 11

Logic - chap. 1 - arguments

Example: (1) And now the great question as to the reason why. (2) Robbery had not been the object of the murder, for (3) nothing was taken. (4) Was it politics, then, or was it a woman? (5) That was the question which confronted me. (6) I was inclined from the first to the latter supposition.

Logic; chapter 1 - slide 12

Logic - chap. 1 - arguments

Example (cont’d): (7) Political assassins are only too glad to do their work and to fly. (8) This murder had, on the contrary, been done most deliberately, and (9) the perpetrator had left his track all over the room, showing that he had been there all the time. (10) It must have been a private wrong, and not a political one, which called for such a methodical revenge.

Logic; chapter 1 - slide 13

Logic - chap. 1 - arguments

(2) Analyze the structure of the argument A strategy

(1) list & number each independent clause

(2) use arrows to indicate the relationship between Ps & Cs

(3) use + to indicate that two premises together entail the conclusion

Logic; chapter 1 - slide 14

Logic - chap. 1 - arguments

(4) use separate arrows to indicate that premises independently support a conclusion

(5) indicate whether several arguments are linked in a series

Logic; chapter 1 - slide 15

Logic - chap. 1 - arguments

Example of portraying the structure of an argument It is rarely economical for

two companies to lay cable in the same area and compete directly. This suggests that cable television is a natural monopoly, and should be regulated by the government.

Logic; chapter 1 - slide 16

Logic - chap. 1 - arguments

Another example (1) I can’t think of anything

more futile than worrying about the past. (2) Did you ever meet anyone who could change the course of past events? (3) Of course not. Past events are entirely outside of human control. (4) Think of all the people who continually worry about their past lives, as if worrying made a difference.

Logic; chapter 1 - slide 17

Logic - chap. 1 - arguments

Example (cont’d): (5) I’m sure that if these people would devote as much time and energy to present opportunities as they spend mulling over the past, they would be far better off. (6) I repeat, it’s futile to worry about the past, (7) because the past is something that can’t be controlled.

Logic; chapter 1 - slide 18

Logic - chap. 1 - arguments

(3) Determine whether the argument is deductive or inductive A traditional way of distinguishing

Deductive general to specific

Inductive specific to general The weakness of this way of

distinguishing between deduction & induction

Logic; chapter 1 - slide 19

Logic - chap. 1 - arguments

An alternative and better way of distinguishing between deduction & induction Induction an argument in

which the conclusion goes beyond the premises and accordingly the relationship between the premises & conclusion is one of probability conclusions go beyond, make

a leap into the unknown

Logic; chapter 1 - slide 20

Logic - chap. 1 - arguments

Deduction an argument in which the conclusion is implicitly contained within the premises and which, accordingly, has a relationship of necessity between the premises & conclusion

The function of deductive arguments to clarify, to make explicit

The function of inductive arguments to lead to new knowledge

Logic; chapter 1 - slide 21

Logic - chap. 1 - arguments

Which of these two types of arguments is better? the tradeoff rigor,

precision, guarantee that the conclusion is true if the premises are true vs new knowledge, discovery, prediction

Logic; chapter 1 - slide 22

Logic - chap. 1 - arguments

Clues for distinguishing between inductive & deductive arguments Look at the kind of claim being

made Deductive arguments often,

not always, move from general to specific; inductive arguments often, not always, move from specific to general To chapter 2