Why Study Logic?

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An Introduction to Formal Logic
Logic is intellectual self-defense against such assaults on reason and also a method of quality control for checking the validity of your own views. But beyond these very practical benefits, informal logic--the kind we apply in daily life--is the gateway to an elegant and fascinating branch of philosophy known as…
Informal Logic and Fallacies
Explore four common logical fallacies. Circular reasoning uses a conclusion as a premise. Begging the question invokes the connotative power of language as a substitute for evidence. Equivocation changes the meaning of terms in the middle of an argument. And distinction without a difference attempts to contrast two positions that…
Introduction to Formal Logic
Having looked at validity in inductive arguments, now examine what makes deductive arguments valid. Learn that it all started with Aristotle, who devised rigorous methods for determining with absolute certainty whether a conclusion must be true given the truth of its premises.
Truth-Functional Logic
Take a step beyond Aristotle to evaluate sentences whose truth cannot be proved by his system. Learn about truth-functional logic, pioneered in the late 19th and early 20th centuries by the German philosopher Gottlob Frege. This approach addresses the behavior of truth-functional connectives, such as "not," "and," "or," and "if"…
First-Order Predicate Logic
So far, you have learned two approaches to logic: Aristotle's categorical method and truth-functional logic. Now add a third, hybrid approach, first-order predicate logic, which allows you to get inside sentences to map the logical structure within them.
Validity in First-Order Predicate Logic
For all of their power, truth tables won't work to demonstrate validity in first-order predicate arguments. For that, you need natural deduction proofs--plus four additional rules of inference and one new equivalence. Review these procedures and then try several examples.
Relational Logic
Hone your skill with first-order predicate logic by expanding into relations. An example: "If I am taller than my son and my son is taller than my wife, then I am taller than my wife." This relation is obvious, but the techniques you learn allow you to prove subtler cases.
Modal Logic
Add two new operators to your first-order predicate vocabulary: a symbol for possibility and another for necessity. These allow you to deal with modal concepts, which are contingent or necessary truths. See how philosophers have used modal logic to investigate ethical obligations.
Three-Valued and Fuzzy Logic
See what happens if we deny the central claim of classical logic, that a proposition is either true or false. This step leads to new and useful types of reasoning called multi-valued logic and fuzzy logic. Wind up the course by considering where you've been and what logic is ultimately…
Logic and Mathematics
See how all that you have learned in the course relates to mathematics--and vice versa. Trace the origin of deductive logic to the ancient geometrician Euclid. Then consider the development of non-Euclidean geometries in the 19th century and the puzzle this posed for mathematicians.
Plato's Heaven - A User's Guide with Professor James Robert Brown of the University of Toronto
What do mathematicians actually do? Just move symbols around or search to uncover undying truths? Most mathematicians shy away from addresing the question, but James Robert Brown, Professor of Philosophy at the University of Toronto plunges straight in to describe his implacable Platonist beliefs.
Introduction to Logical Concepts
Practice finding the logical arguments hidden in statements by looking for indicator words that either appear explicitly or are implied--such as "therefore" and "because." Then see how to identify the structure of an argument, focusing on whether it is deductive or inductive.