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Reasoning and Critical Thinking - PHI1101

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University of Ottawa
Laura Byrne

PHI1101D - Reasoning and Critical Thinking September 7 2011 - Lecture 1 Unit One: Reasoning and Critical Thinking Epistemology Episteme - knowledge/science Are there limits to human knowledge? Can we understand the world as it really is objectively? Metaphysics Does God exist? Is the will free Logic What are the correct forms of reasoning? Critical Thinking The application of logic to arguments in ordinary language The Method of Philosophy Reasoned argument (no creativity, no revealed text [Bible], no traditions) non- philosophical What makes an argument convincing? The Ontological Argument Anselm 1033 - 1109 A.D. Become Archbishop of Canterbury Can what is known on the basis of faith be philosophical? Start with the denition of God What makes a good denition? God is something than which nothing greater can be thought (premise one) Existence in reality is greater than existence in the mind alone (e.g. mental money vs. real money) (premise two) Conclusion: Therefore God exists in reality September 9 2011 - Lecture 2 PHI1101D - Reasoning and Critical Thinking The Basic Concepts of Critical Thinking and Their Logical Properties Concepts Properties Statements True or false Sets Consistent or inconsistent Logically strong or logically weak. Arguments Sound or unsound. Noot argumeentts notttueeorrfase.. Statements The most basic concept of critical thinking Sentence used to make a claim Capable of being either true or false Statement: Test Tip Logic calls them assertions or propositions When asking whether something is a statement or not: Two Laws of Logic 1. This is (not) a statement 1. The Law of Non-Contradiction 2. The Law of the Excluded Middle (or The Law of 2. A statement is used to make a claim Bivalence) and is capable of being T/F 3. Say what it is (if not a statement) 4. (not) Capable of being true or false Socrates is a man proposition p Socrates is not a man negation not-p (~p or -p) Example: Lassie is a dog = p Lassie is not a dog = not-p 1. The Law of Non-Contradiction States that it is not impossible for both a proposition and its negation to be true at the same time Cannot assert p and not-p at the same time Contradictions (p and not-p) cannot be true P and not-p cannot coexistPHI1101D - Reasoning and Critical Thinking Paradox: A statement or proposition that, despite sound reasoning from acceptable premises, leads to a conclusion that seems senseless, logically unacceptable or self- contradictory 2. The Law of the Excluded Middle (or The Law of Bivalence) Every proposition must be either true or false Any middle position between true and falsity is excluded Black and white No grey area If a proposition is true, its negation must be false and vice versa If p is true, not-p must be false Fuzzy logics Innite values ish Sets of Propositions Sets Propositions can be combined in groups or sets E.g. Lassie is a dog. Lassie barks. Consistency Consistency: Test Tip A set is consistent if and only if it is possible for When answering a question asking if a set the sentences in that set to be true at the same time is consistent
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