5: Logic
- Page ID
- 113156
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Logic is, basically, the study of valid reasoning. When searching the internet, we use Boolean logic – terms like “and” and “or” – to help us find specific web pages that fit in the sets we are interested in. After exploring this form of logic, we will look at logical arguments and how we can determine the validity of a claim.
The material in this chapter is from Math In Society by David Lippman.
- 5.1: Logic Statements
- Logic is the study of the methods and principles of reasoning. In logic, statement is a declarative sentence that is either true or false, but not both. The key to constructing a good logical statement is that there must be no ambiguity. To be a statement, a sentence must be true or false. It cannot be both. In logic, the truth of a statement is established beyond ANY doubt by a well-reasoned argument.
- 5.2: Truth Tables- Conjunction (and), Disjunction (or), Negation (not)
- Because compound statements can get tricky to think about, we can create a truth table to keep track of what truth values for the simple statements make the compound statement true and false. A truth table is a table showing what the resulting truth value of a compound statement is for all the possible truth values for the simple statements.
- 5.3: Truth Tables- Conditional, Biconditional
- A conditional is a logical compound statement in which a statement 𝑝 , called the antecedent, implies a statement 𝑞 , called the consequent.
- 5.4: Arguments with Truth Tables
- Logic is the study of the methods and principles of reasoning. An argument is a set of facts or assumptions, called premises, used to support a conclusion. For a logical argument to be valid, it is the case that, if the premises are true then the conclusion must be true.
- 5.5: Forms of Valid and Invalid Arguments
- Rather than making a truth table for every argument, we may be able to recognize certain common forms of arguments that are valid (or invalid). If we can determine that an argument fits one of the common forms, we can immediately state whether it is valid or invalid.
- 5.6: Arguments with Euler Diagrams
- We can interpret a deductive argument visually with an Euler diagram, which is essentially the same thing as a Venn diagram, where we use circles to represent statements. This can make it easier to determine whether the argument is valid or invalid.
- 5.7: Logical Fallacies in Common Language
- In a previous section, we saw that logical arguments can be invalid when the premises are not true, when the premises are not sufficient to guarantee the conclusion, or when there are invalid chains in logic. There are a number of other ways in which arguments can be invalid, a sampling of which are given here.
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