1. Philosophy : Thinkers, Theories and Questions Chapter 2
Informal Logic
Philosophy : Thinkers, Theories and Questions
Chapter 2

2. Introduction
Informal logic focuses on the kinds of arguments that are used in everyday contexts such as conversations, newspaper editorials, debates and philosophical passages
These are logical in the sense that they adhere to the law of non- contradiction

3. Arguments must also be cogent
Meanings of the terms are clear and appropriate
The premises are accepted as true
The premises are judged as giving strong support for the conclusion
To gauge the cogency of an argument we judge the strength of support that the premises give to a conclusion
If an argument is not cogent then it has likely committed an informal fallacy

4. Dissecting an Argument Using Informal Logic
Informal logic involves two steps:
1) indentifying premises and conclusions in the reconstruction or interpretation of arguments
2) using a fallacy toolkit to examine the relevance or truth of the premises, the way that terms are used, and the connection between premises and conclusions

5. E.g.: They are starting about seatbelts again, but if the law is passed, I will be the first to demand a cell in jail. I will not wear a seat belt. Eleven years ago, I was thrown into the windshield when my van went into a seven foot ditch filled with five feet of water. Quick thinking by a farmer, who dived into the water and got me out, saved my life. Had I been wearing a seatbelt, there is no way he could have undone it and rescued me. I have suffered daily and spent more time in hospital than out, but I’m still alive. The seat belt law is one of the reasons I miss the beautiful drives through Canada. Reprinted in Logical Self-Defence

6. Step 1: Identifying Premises and Conclusions
Sub argument 1
P1: I was an accident in which I would have died had I been wearing a seat belt.
C: Therefore, seat belts can cause death.
Sub argument 2
P1: One ought to break laws mandating the use of devices that can cause death.
P2: Seat belts are devices that can cause death.
C: Therefore, one ought to break laws mandating the use of seat belts.

7. Much of the extraneous material has been omitted and a hidden premise has been added
P1 of sub argument 2
This premise is required to bridge the gap between the conclusion of the first sub argument and the second
The conclusion in the first sub argument is also a premise for the second sub argument

8. Step 2: Using the fallacy toolkit
A fallacy is an argument that may seem to be cogent but that proves, upon examination, not to be cogent and the conclusion should not be accepted for the reasons given
The seatbelt argument is subject to two fallacies: problematic premise and hasty generalization

9. The Fallacy of Problematic Premise
Are the premises of the argument true?
Does the author know for certain that he would have died? Could a different scenario have unfolded? Could the seat belts have prevented him from going through the windshield, would he have remained conscious and been able to get himself out of the van?
The fallacy of problematic premise judges whether the premises should be accepted as true
So this can be charged to almost any argument
Some guidelines for problematic premise
The premise must not contradict other propositions that you hold as true
If a premise is asserting facts about the world, the assertion should be in agreement with your own experiences and/or observations.
If a premise is based on something you have read or heard the source must be credible

10. The Fallacy of Hasty Generalization
Since the argument uses one accident for a rule that applies to what happens in general he commits the fallacy of hasty generalization
If we accept the first argument, then seat belts can endanger lives but do they endanger lives in general

11. The Principle of Charity
The principle of charity states that an argument should be given the best interpretive light by making a sincere effort to reconstruct what the author is saying in a way that is true to the text and errs on the side of cogency
If the reconstruction is inconsistent with the text and re-interpreted into a les plausible form then the logician has committed the fallacy of straw man