Lecture 3: Reasoning and Logic

1. Lecture 3: Reasoning and Logic

2. Recap

3. Recap • In our previous lecture we: • Looked at the origins of philosophy • Investigated Thales’ metaphysical theory that everything is composed of water. • Contrasted the rational thinking (logos) of Thales with the mythical thinking (mythos) of his predecessors. • Discussed in further detail the similarities and differences between science and philosophy • Discussed the methodological differences between science and philosophy • Concluded by discussing the value of philosophy

4. Recap • Unresolved Discussions: • Q: Does ‘philosophy’ change over time? • Throughout its history, science has undergone numerous changes • These changes have often had big influences on society, philosophy etc. • Possible answers include: Rationalism “The view that affirms reason, with its interest in evidence, examination, and evaluation, as authoritative in all matters of belief and conduct”(Miller, Ed L. Questions that Matter, 2009. p.10)

5. Recap • Unresolved Discussions: • Q: Should we view religious texts and religions as based on mythical or rational thinking? • Points for discussion: • Some scientists might, for example, claim that religious belief is governed entirely by mythical thinking. • The appeal to supernatural beings might suggest a mythical dimension. • Some philosophers, anthropologists, sociologists, etc. have asked whether the distinction between mythical and rational thinking is valid. In particular they ask whether the distinction is culturally biased. • Remember! Just because an account discusses God does not necessarily make it mythical! Rationalism “The view that affirms reason, with its interest in evidence, examination, and evaluation, as authoritative in all matters of belief and conduct”(Miller, Ed L. Questions that Matter, 2009. p.10)

6. Recap • Unresolved Discussions: • Q: Should we view religious texts and religions as based on mythical or rational thinking? • Possible answer: There are different ways of investigating the same thing • For example, we could investigate the Bible in the following ways: Rationalism “The view that affirms reason, with its interest in evidence, examination, and evaluation, as authoritative in all matters of belief and conduct”(Miller, Ed L. Questions that Matter, 2009. p.10)

7. Logic and Reasoning

8. Today’s Lecture In today’s lecture we will: Investigate an important tool used by philosophers: logic and reasoning Examine the form of logic Attempt to understand the distinction between Deductive and Inductive reasoning. Outline and examine a number of important argumentative fallacies (invalid ways of arguing) Apply what we have learned using a number of examples. Conclude our investigation into the what/who/why/how of philosophy.

9. Logic & How Not to Argue • Philosophers often use logic to examine and evaluate arguments: • Logic is “The Formal Study of Valid Inferences” • Distinguishes between valid and invalid arguments • Also distinguishes between Sound and Unsound arguments • Powerful tool for analysis and criticism. • Analyzes the logical structure of an argument (not the truth of an argument) Logical and Reasoning

10. Two Forms of Reasoning Deductive Reasoning In a valid deductive argument; if the premises are true, the conclusion must be true, by virtue of a logically necessary inference. [Deductive arguments tend to argue from the whole to the particular] Inductive Reasoning In a strong inductive argument: if the premises are true, the conclusion is probably true, by virtue of a supportive inference. [Inductive arguments tend to argue from the part to the whole] (Miller, Ed L. Questions that Matter, 2008. p.23) Logical and Reasoning

11. A little clarification Valid Arguments Valid arguments display proper deductive form True Statements True statements are possible in any argument regardless of form Sound Arguments Sound arguments have both valid form and true premises (Miller, Ed L. Questions that Matter, 2008. p.19) Logical and Reasoning

12. Deductive Reasoning

13. Deductive Reasoning Deductive Reasoning All men are mortal Socrates is a man Therefore Socrates is mortal Premises Conclusion The premises logically entail the conclusion The argument is valid and sound(Both true and logically valid)

14. Deductive Reasoning An example of a deductive, logical argument All A’s are B’s S is an A Therefore S is a B Remember: If the premises of a deductive argument are true the conclusion must be true!

15. Deductive Reasoning Is this argument logically valid? All ducks float on water Professor Harris is a duck Therefore Professor Harris floats on water Do the premises logically entail the conclusion? Is the argument true? Is the argument sound? (is it logically valid and true?)

16. Deductive Reasoning How about this one? If it is raining then the streets are wet The streets are wet Therefore it is raining Do the premises logically entail the conclusion? Is the argument true? Is the argument sound? (is it logically valid and true?)

17. Inductive Reasoning

18. Inductive Reasoning An example of an inductive, argument Instance 1 of A is observed to be X Instance 2 of A is observed to be X Instance 3 of A is observed to be X Instance 4 of A is observed to be X Instance 5 of A is observed to be X ... Therefore, all A is X

19. Inductive Reasoning An example of inductive reasoning: Universal Generalization Swan 1 is white Swan 2 is white Swan 3 is white Swan 4 is white Swan 5 is white Swan 526 is white ... Therefore all swans are white Do the premises give supportive inference to the conclusion? Is the argument true? Is the argument sound? (is there sufficient supportive inference and is the argument true?)

20. Inductive Reasoning Another example of inductive reasoning: Analogy A is observed to be X and Y B is observed to be X and Y C is observed to be X and Y D is observed to be X and Y ... M is observed to be X Therefore, M is Y Do the premises give supportive inference to the conclusion? Is the argument true? Is the argument sound? (is there sufficient supportive inference and is the argument true?)

21. Summary

22. Deductive Reasoning In a valid deductive argument; if the premises are true, the conclusion must be true, by virtue of a logically necessary inference. Inductive Reasoning In a strong inductive argument: if the premises are true, the conclusion is probably true, by virtue of a supportive inference. Valid Arguments Validarguments display proper deductive form True Statements True statements are possible in any argument regardless of form Sound Arguments Sound arguments have both valid form and true premises

23. Logical Fallacies

24. Some more clarification Formal Fallacies Mistakes in reasoning due to a failure in following the rules for the formal structure of valid arguments. These fallacies do not concern truth or falsity but validity. Informal Fallacies Mistakes in reasoning due to carelessness regarding relevance and clarity of language. These fallacies bear directly on issues of truth and falsity. (Miller, Ed L. Questions that Matter, 2008. p.23) Logical Fallacies

25. Argumentative Fallacies Loaded Language is language with the sole purpose of swaying the emotions of the audience for or against an argument. Equivocation occurs when a word or expression changes its meaning in the course of an argument, sometimes referred to as a “weasel word.” Begging the Question occurs when the conclusion of an argument is already present, usually disguised, in one of its premises. Ad Hominem (appeal to the person) irrelevantly attacks the person making a claim rather than attacking the claim itself. Straw Man Inappropriately simplifies an opposing argument so that it becomes a cartoon or caricature of the true argument and is easy to refute. “Person who” is the fallacy of generalizing or drawing a conclusion from too little information. Also called a hasty induction. Ad populam (appeal to the masses) seeks to strengthen a claim by an emotional appeal to the passions and prejudices of the listeners. Ad ignorantium (appeal to ignorance) affirms the truth of something on the basis of the lack of evidence to the contrary. False Dilemma involves limiting the options considered to only two in a way that is unfair to the person facing the dilemma. Logical Fallacies (Miller, Ed L. Questions that Matter, 2008. pp. 22-24)

26. Topic Conclusion

27. What is Philosophy? A rational investigation into a range of topics and aspects of human existence Who does Philosophy? Everyone, particularly anyone that asks philosophical questions. Why do we do Philosophy? Many philosophical inquiries are important. Not everything can be investigated scientifically. Philosophy can provide us with important skills and knowledge. How do we do Philosophy? Philosophers use reason and rational thinking as their principle means of conducting their inquiries; including logic; arguments; discussion; observation; evaluation and more... Topic Conclusion

28. Recap • Conclusions: • Some questions do not have any definite answers but are still valid questions! • Philosophy can be useful tool for critically examine the assumptions implicit in other systems of thought. • Philosophy is a useful tool for examining the world. (beyond the natural sciences. • Like any tool, Philosophy has a limited role and application.

29. Over the coming weeks we will be investigating: • What is Reality? (Metaphysics/Ontology) • (a) What is the relationship between mind and body? • Theory of Knowledge (Epistemology) • Natural Theology • Moral Philosophy Upcoming topics

30. Perhaps ‘Philosophy’ Consists of “Family Resemblances” And we can go through many, many other groups of games in the same way; can see how similarities crop up and disappear.And the result of this examination is: we see a complicated network of similarities overlapping and criss-crossing: sometimes overall similarities, sometimes similarities of detail.I can think of no better expression to characterize these similarities than “family resemblances”: for the various resemblances between members of a family: build, features, colour of eyes, gait, temperament, etc. etc. overlap and criss-cross in the same way.—And I shall say “games” form a family. Ludwig Wittgenstein, Philosophical Investigations, (New York: Macmillan, 1964), p.32 Topic Conclusion

31. Discussion

32. Discussion • Questions for Discussion: • Is the distinction between mythical and rational thinking valid? Or does modern science constitute another form of myth-making? • Could science do without philosophy or vice versa? • Defend one of these views: • “Philosophy” can be defined. • “Philosophy” cannot be defined. • Is philosophy a worthwhile subject? • What is significant about the form of deductive arguments?