Propositional Logic Fundamentals
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Questions and Answers

Which of the following best describes the Law of Excluded Middle?

  • Things must be identical with themselves.
  • A statement can be both true and false simultaneously.
  • Every proposition must be either true or false, but not both. (correct)
  • Logically correct propositions can affirm and deny the same thing.

The statement 'x > 10' is a proposition.

False (B)

Explain the Law of Identity in propositional logic using the variable 'A'.

A = A

In propositional logic, a proposition is a declarative sentence that is either true or _____.

<p>false</p> Signup and view all the answers

Match each of the following laws of thought with its description:

<p>Law of Identity = A thing is identical to itself. Law of Excluded Middle = Every proposition must be either true or false. Law of Non-Contradiction = A proposition cannot be both true and false.</p> Signup and view all the answers

Which symbol represents the negation of a proposition?

<p>~ (A)</p> Signup and view all the answers

A conjunction is true if at least one of the propositions is true.

<p>False (B)</p> Signup and view all the answers

Which of the following statements violates the Law of Non-Contradiction?

<p>The car is both moving and stationary. (D)</p> Signup and view all the answers

If proposition A is false and proposition B is true, what is the truth value of the disjunction A v B?

<p>true</p> Signup and view all the answers

Which of the following uses numerical symbols to represent a false statement?

<p>0 (B)</p> Signup and view all the answers

Given P = 'Today is Monday' and Q = 'The sky is blue', which of the following scenarios violates the Law of Excluded Middle?

<p>P is both true and false. (D)</p> Signup and view all the answers

The combined proposition called a ______ will be true if one of the propositions is true.

<p>disjunction</p> Signup and view all the answers

Given proposition P: 'The sky is blue' and proposition Q: 'Grass is green', which of the following correctly represents the conjunction of P and Q?

<p>The sky is blue and grass is green. (B)</p> Signup and view all the answers

If proposition A is 'It is sunny' and proposition B is 'I am happy', then the disjunction A v B is only true if it is sunny.

<p>False (B)</p> Signup and view all the answers

Provide the truth table result for A ^ B when A is true and B is false.

<p>false</p> Signup and view all the answers

Match the logical operation with its corresponding condition for a TRUE result:

<p>Negation = Original proposition is FALSE Conjunction = Both propositions are TRUE Disjunction = At least one proposition is TRUE</p> Signup and view all the answers

Given the implication 'If it is raining, then the ground is wet,' which of the following represents the converse?

<p>If the ground is wet, then it is raining. (D)</p> Signup and view all the answers

In a biconditional statement, both propositions must have the same truth value (either both true or both false) for the entire statement to be considered true.

<p>True (A)</p> Signup and view all the answers

What is the symbol used to represent a biconditional statement?

<p>A ↔ B</p> Signup and view all the answers

In the implication A → B, A is referred to as the ________ and B is the _________.

<p>antecedent, consequence</p> Signup and view all the answers

Match each type of implication with its correct description:

<p>Implication (A → B) = If A, then B Converse (B → A) = If B, then A Inverse (~A → ~B) = If not A, then not B Contrapositive (~B → ~A) = If not B, then not A</p> Signup and view all the answers

Which of the following statements accurately describes the truth conditions for an XOR (exclusive or) operation between two propositions?

<p>XOR is true when exactly one of the propositions is true. (D)</p> Signup and view all the answers

Given the implication: 'If a shape is a square, then it has four sides.' Which of the following is the contrapositive of this statement?

<p>If a shape does not have four sides, then it is not a square. (A)</p> Signup and view all the answers

The antecedent in an implication is the 'then statement'.

<p>False (B)</p> Signup and view all the answers

Which of the following best describes the purpose of a truth table?

<p>To keep track of all possible combinations of truth values for variables in a proposition. (C)</p> Signup and view all the answers

The statement x > 10 is always a proposition, regardless of the value of x.

<p>False (B)</p> Signup and view all the answers

What is the fundamental difference between a statement and a proposition?

<p>A proposition is a statement that is either true or false, while a statement can be a question, command, or opinion that doesn't have a truth value</p> Signup and view all the answers

Combining propositions using the keyword not is an example of a logical connective called a ______.

<p>negation</p> Signup and view all the answers

Match the logical scenario with its corresponding truth table result, given that 'A' represents 'age between 18-65' and 'B' represents 'fully vaccinated', and 'C' represents conditional to go out.

<p>A = True, B = True = C = True A = True, B = False = C = False A = False, B = True = C = False A = False, B = False = C = False</p> Signup and view all the answers

Which of the following is the correct interpretation of the logical connective 'and'?

<p>The compound proposition is true only if both propositions are true. (D)</p> Signup and view all the answers

Which of the following is a compound proposition?

<p>She is tall and he is short. (A)</p> Signup and view all the answers

If proposition A is 'The sky is blue' and proposition B is 'Grass is green,' then the compound proposition 'A and B' is true.

<p>True (A)</p> Signup and view all the answers

What is the result of $A \oplus B$ (A XOR B) when A is false and B is true?

<p>True (A)</p> Signup and view all the answers

According to the truth table, if A is true and B is false, then $A \rightarrow B$ (if A then B) is true.

<p>False (B)</p> Signup and view all the answers

What is the result of $A \land B$ (A and B) when A is true and B is true?

<p>true</p> Signup and view all the answers

In a truth table, the symbol '~' represents the logical operator called ______.

<p>negation</p> Signup and view all the answers

Match the logical operator to the description of its output:

<p>$A \land B$ = True only when both A and B are true $A \lor B$ = True if either A or B (or both) are true $A \oplus B$ = True if A and B have different truth values $A \leftrightarrow B$ = True if A and B have the same truth value</p> Signup and view all the answers

When is $A \rightarrow B$ (If A then B) false?

<p>When A is true and B is false (A)</p> Signup and view all the answers

Which logical operator has the highest precedence?

<p>Negation (D)</p> Signup and view all the answers

The biconditional operator ($A \leftrightarrow B$) is true when A and B have different truth values.

<p>False (B)</p> Signup and view all the answers

Which of the following statements accurately describes a tautology in logic?

<p>A statement that is always true, regardless of the truth values of its components. (C)</p> Signup and view all the answers

The statement 'B ∧ ¬B' is a contradiction.

<p>True (A)</p> Signup and view all the answers

Define logical equivalence in your own words.

<p>Two compound propositions are logically equivalent if they have the same truth value in every possible case.</p> Signup and view all the answers

A statement that is neither a tautology nor a contradiction is called a __________.

<p>contingency</p> Signup and view all the answers

Match each type of logical statement with its defining characteristic:

<p>Tautology = Always true Contradiction = Always false Contingency = Sometimes true, sometimes false</p> Signup and view all the answers

Which of the following accurately describes a 'contingency'?

<p>A statement that is true only under certain conditions. (D)</p> Signup and view all the answers

If two compound propositions, P and Q, are logically equivalent, which of the following statements must be true?

<p>P and Q have the same truth value in all possible cases. (B)</p> Signup and view all the answers

If a statement is a tautology, then its negation is a contradiction.

<p>True (A)</p> Signup and view all the answers

Flashcards

Proposition

A declarative sentence that is either true or false, but not both.

Propositional Representation

Representing a proposition using a capital letter.

Truth Value: T/1

Representing a 'true' statement

Truth Value: F/0

Representing a 'false' statement

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Law of Identity

Everything is identical to itself.

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Law of Excluded Middle

Every proposition is either true or false.

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Law of Non-Contradiction

A proposition cannot be both true and false.

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Statement Analysis

Indicates if a statement is a proposition and its truth value.

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Truth Table

A chart that shows all possible truth values for a proposition.

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Compound Proposition

A proposition formed by combining one or more propositions.

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Negation

A logical connective that reverses the truth value of a proposition.

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Greater Than (>)

Represented by the symbol '>'. It asserts that one value is greater than another.

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Less Than (<)

Represented by the symbol '<'. Indicates one value is smaller than the other.

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Proposition truth value dependency

A proposition's truth depends on a variable's value.

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Logical Connectives

Combining propositions with keywords like 'and', 'or', or 'not'.

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Conjunction

Combined proposition that is only true if both propositions are true.

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Disjunction

Combined proposition that is true if at least one proposition is true.

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Negation Symbols

Uses the symbol ( ~ ) or ( ¬ ) attached to the representation of the proposition.

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Conjunction Symbol

The symbol (^) is used to represent the word and in a conjunction.

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Disjunction Symbol

The symbol (v) is used to represent the word or in a disjunction.

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Proposition Value

Proposition whose value is either True (T) or False (F).

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Antecedent

The first proposition in an implication.

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Consequence

The proposition that follows the antecedent in an implication.

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Implication

A statement that one proposition implies another (A → B).

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Converse

Reverses the implication: B → A.

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Contrapositive

Negates and reverses the implication: ~B → ~A.

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Inverse

Negates the original implication: ~A → ~B.

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Biconditional

A statement true if and only if both propositions have the same truth value (A ↔ B).

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Exclusive Or (XOR)

True if one proposition is true, but not both. Symbol: ⊕

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Conjunction (A ∧ B)

True only if both A and B are true.

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Disjunction (A ∨ B)

True if either A or B (or both) are true.

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Exclusive Disjunction (A XOR B)

True if A and B have different truth values.

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Implication (A → B)

False only if A is true and B is false. Otherwise, it's true.

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Biconditional (A ↔ B)

True only if A and B have the same truth value (both true or both false).

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Precedence of Logical Operators

The order in which logical operations are performed. Determines the overall truth value of a complex proposition.

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Tautology

A statement that is always TRUE, no matter the truth values of its parts.

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Contradiction

A statement that is always FALSE, regardless of the truth values of its parts.

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Contingency

A statement that can be either TRUE or FALSE depending on the truth values of its parts.

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Logical Equivalence

Two statements are logically equivalent if they have the same truth value in every possible case.

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A ^ ~A

A logical statement formed using operators like AND (^).

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A v ~A

A logical statement formed using operators like OR (v).

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Conditional Indicator (→)

It returns ‘false’ only when A is true and B is false; otherwise, it returns ‘true’.

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Neither Tautology nor Contradiction

If the results are a mix of true and false.

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Study Notes

  • A proposition is a statement that can be proven, explained, or discussed, and is either true or false (but not both).
  • Capital letters usually denote propositions in tables.
  • T represents a true statement.
  • F represents a false statement.
  • 1 represents true, 0 represents false.

Bases for Propositional Logic

  • Scholars in the 18th, 19th, and early 20th centuries considered the "laws of thought" as the basis of all logic.
  • Law of Identity: Things are identical to themselves (P = P); water is water.
  • Law of Excluded Middle: Every proposition is either true or false, not both, and not neither.
  • Law of Non-Contradiction: Correct propositions cannot affirm and deny the same thing.

Truth Table

  • Used to keep track of proposition possibilities.
  • Each row lists a possible combination of true and false values for each variable, indicating whether the statement is true.

Compound Proposition

  • Combining one or more existing propositions creates a compound proposition.

Types of Logical Connectives

  • Negation: Uses "not" to state the opposite of a proposition, indicated by the symbol (~) or (-).
  • Conjunction: Combines propositions using "and;" true only if both propositions are true, represented by the symbol (^).
  • Disjunction: Combines propositions using "or;" true if at least one proposition is true, represented by the symbol (v).
  • Implication: "If-then" statements; the first proposition is the antecedent, and the second is the consequence, symbolized by an arrow (→).
    • Converse: Reverse of the implication (B → A).
    • Contrapositive: Negates and interchanges propositions (~B → ~A).
    • Inverse: Negates the propositions (~A → ~B).
  • Biconditional: Combines a conditional statement with its converse, using "if and only if," symbolized by (↔); both propositions must have the same truth value (TT or FF) to be true.
  • XOR (exclusive or): A version of disjunction that does not allow both propositions to be true simultaneously, symbolized by (⊕).

Truth Table Reference

  • Can be used as a guide when working with truth tables.
  • Summarizes the truth values for the logical connectives: negation, conjunction, disjunction, exclusive disjunction, implication and biconditional.

Precedence of Logical Operators

  • Establishes an order for solving complex propositions.
  • From highest to lowest precedence: Negation (~), Conjunction (^), Disjunction (v), Implication (→), and Biconditional (↔).

Tautology

  • A statement that is always true, regardless of the truth values of its parts.

Contradiction

  • A statement that is always false, regardless of the truth values of its parts.

Contingency

  • A statement that is neither a tautology nor a contradiction.

Logical Equivalence

  • Two compound propositions with the same truth value in every case, denoted by the symbol ≡.

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Propositional Logic PDF

Description

Explore the fundamental principles of propositional logic, including the Law of Excluded Middle, the Law of Identity, and the Law of Non-Contradiction. This lesson covers propositions, conjunctions, disjunctions, and how to evaluate their truth values.

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