1. Patterns of Informal Non-Deductive Logic (Ch. 6)

2. Non-Deductive Arguments1
Chapter 6

3. Non-Deductive Arguments
Non-Deductive /Inductive arguments: If the premises are true, the conclusion is NOT necessarily/guaranteed true

4. Non-Deductive Arguments
Non-deductive arguments cannot give proofs
All non-deductive arguments are invalid, but there are good and bad ones
Non-deductive arguments fall on a scale from strong to weak
Strong: a non-deductive argument where the conclusion is probably true assuming the premises are true
Weak: a non-deductive argument where the conclusion is probably not true assuming the premises are true
Cogent argument: strong argument AND premises are true
Cogent arguments are good non-deductive!

5. Overview Deductive Arguments Non-Deductive Arguments Sound Cogent
Stronger
Weaker
Valid
Invalid
Valid Arg: sound or unsound
Invalid Arg: always unsound
Strong Arg: cogent or uncogent
Weak Arg: always uncogent

6. Kinds of Non-Deductive Arguments1
Chapter 6

7. Inductive Generalization
Generalization: premises about particulars, general conclusion.
Example: Inductive Generalization
One swan is white
Another swan is white …
So, all swans are white
This is a cogent argument: strong with true premises
strong because the conclusion is probable assuming the premises are true
the premises are all true

8. Revising Inductive Generalizations
For centuries in Europe, it was thought that there were only white swans. So, the above argument looked like it produced a true conclusion. Later, black swans were discovered in Australia. So, in fact, the conclusion is false. However, the argument is still a cogent one (strong with true premises)
We can revise the argument now to include the new evidence and give a stronger argument
One swan is white
Another is white
Another is black …
So, all swans are black or white

9. Induction but not a generalization
Induction can also have a particular conclusion (about a specific thing not all)
The textbook calls some of these “arguments from past experience”
Example
One swan is white
Another swan is white …
That one swan over there by the lake is white

10. Faulty Inductive Generalization
Inductive Generalizations are faulty when
i) there are not enough samples (i.e. particular premises)
For example, if we concluded that all swans are white after observing two swans, the sample size would be way too small.
ii) the samples are not representative
For example, if we looked at swans that we covered in blue paint at a circus. Even if we observed many cases of blue swans at a circus, the sample would not be a representative one.

11. Argument by Analogy
Argument by analogy: two things are similar in some respects, so they are similar in some other respect
A has characteristic W, X, Y
B has characteristic W, X, Y
A has characteristic Z
So, B probably has characteristic Z
Example
Earth has oxygen, hydrogen and water
Mars has oxygen, hydrogen and water
Earth has life
So, Mars has life

12. Fallacy of Weak Analogy
When the characteristics compared in premises are irrelevant to characteristic of conclusion
Example
Child pornography is sold and distributed
Newspapers are sold and distributed
Child pornography should be outlawed
So, newspapers should be outlawed

13. 3 Views on the Existence of God
Theism: I know that God exists: I have a good argument that God exists
Atheism: I know God does not exist: I have a good argument that God doesn’t exist
Agnosticism: I don’t know whether God exists: I don’t have a argument either way.
Arguments
One argument by analogy for theism: The argument from design
One deductive argument for atheism: the problem of evil
One inductive argument for atheism: the problem of evil

14. Design Argument for the Existence of God
The Argument from Design
A watch is finely-tuned, complex, So a watch has a designer
The Universe is finely-tuned, highly complex.
So, the world has a designer by a designer (God)
Objection:
the watch and the world are not remotely similar. We know just about everything about how a watch works (e.g. what happens when you drop it in watter, what its parts do, etc.), but we know almost nothing about the Universe (how did it start, can it be destroyed, does it end, etc.). Because the world and the watch are so very different we cannot make the analogy

15. Deductive Argument that God Doesn’t Exist
The Problem of Evil Argument
Suppose God exists Hypothesis
God knows about all evil that has or will happen
God can do anything
God is good: he eliminates as much evil as he knows about and can
So, God knows about all evil and eliminates all evil. from 1-3
So, there is no evil in the world from A,5 7
But, there is evil in the world (earthquakes, WW2) Premise
Since 5 and 6 contradict, A. must be false
So, God does not exist

16. Objection
The Problem of Evil Argument is a proof that God doesn’t Exist; It shows that any evil is impossible if God exists, because he would have prevented it from happening
Objection: God gave us freedom
He does not help us because he wants us to make our own choices. He knew about WW2, and Indonesian Tsunami but let it happen anyway because it is better for humans to make their own choices (to be tested and deal with loss) than to have a world where humans do not make free choices
Premise 6 is false: Earthquakes, WW2 are not evils.

17. Inductive Argument from Evil
Many are convinced by “Freedom Objection” to the Deductive Argument. There are other, non-deductive arguments that God does not exist.
Even if we assume that God gave us freedom, why must WW2 have happened or the Indonesian Tsumani or many other similar events. This argument collects as evidence those cases and argues that probably God does not exist
The Inductive Argument from Evil
Indonesian Tsunami is an evil preventable for God
WWII is an evil preventable by God … ….
So, God does not exist