Section A General Questions about Logic Flashcards
- What is the difference between inclusive and exclusive disjunction?
The disjunction of two propositions, p or q, is represented in logic by p ∨ q. This is evaluated as true if both p and q are true, and is called inclusive disjunction. A different notion, exclusive disjunction, is defined true only when exactly one of p, q is true, and as false if they are both true.
- What is the major operator of a complex propositional function?
If a sentence has only one logical operator, then that is the main operator. If a sentence has more than one logical operator, then the main operator is the one outside the parentheses.
- Why do ‘only if’ clauses go into the consequent of conditionals?
only if statements are exclusive propositions, when this kind of statement gets translated as a conditional the class term after “only” becomes the consequent
- Give a propositional logic translation of the following form: A or B, but not both.
(A v B) * ~(A * B)
- Explain why the following two propositional logic claims are equivalent: A ≡ B and (A ⊃ B) * (B ⊃ A).
If A then B, so this turns in to B; If B then A, so this turns into A. The final form is B * A. This is equivalent to A ≡ B because for both claims A and B both have to be true for the statement to be. If either A or B is false then the entire statement is false.
- Give an example of Modus Ponens in natural language.
If today is Tuesday, then John will go to work.
Today is Tuesday.
Therefore, John will go to work.
- Give an example of Modus Tollens in natural Language.
If you give up cigarettes, then you care about your health.
You did not give up cigarettes.
Therefore, you do not care about your health.
- Show with a truth table why Modus Ponens is a valid inference form.
P Q If P, then Q
T T T
T F F
F T T
F F T
- Show with a truth table why Modus Tollens is a valid inference form.
P Q If P then Q Not Q Therefore, not P
T T T F F
T F F T F
F T T F T
F F T T T
- Show with a truth table why Asserting the Consequent is an invalid inference form.
Asserting the Consequent:
1. If A then B
2. B
3. Therefore, A
P Q If P, then Q Q is true Therefore, P is true?
T T T T T
T F F F F
F T T T F
F F T F F
- Show with a truth table why Negating the Antecedent is an invalid inference form.
Denying the antecedent, sometimes also called inverse error or fallacy of the inverse, is a formal fallacy of inferring the inverse from the original statement. It is committed by reasoning in the form:
If P, then Q.
Therefore, if not P, then not Q.
P Q If P then Q If not P then not Q
T T T F
T F F T
F T T T
F F T T
- Show with a truth table why Double Negation is a valid replacement rule.
P ¬P ¬(¬P)
T F T
F T F
- Explain the following sentence: doing a proof is a way of demonstrating syntactic validity in Propositional
Logic.
In Propositional Logic, a proof is a systematic way of demonstrating that a particular statement, called a proposition, can be derived from a set of premises using a set of rules of inference. The statement “doing a proof is a way of demonstrating syntactic validity in Propositional Logic” means that when a proof is performed in Propositional Logic, it shows that the proposition being proved is syntactically valid, meaning that it follows the rules of the formal language of propositional logic.
In other words, a proof provides a rigorous demonstration that the conclusion of an argument is logically valid based solely on the structure of the argument, without considering the truth or falsity of its propositions. By constructing a proof, we can determine if a statement follows logically from the premises or if it violates the rules of syntax of propositional logic. Thus, doing a proof is an essential tool for establishing the validity of propositions in propositional logic.
- Explain the following sentence: the negation of a tautology is a self-contradiction
A tautology is a statement that is always true, regardless of the truth values of its individual components. For example, the statement “either it is raining or it is not raining” is a tautology, because it is true no matter what the weather conditions are.
The negation of a tautology is a statement that is always false, regardless of the truth values of its individual components. For example, the negation of the tautology “either it is raining or it is not raining” is “it is both raining and not raining at the same time,” which is a self-contradiction because it is impossible for something to be true and false at the same time and in the same sense. Therefore, the negation of a tautology results in a statement that contradicts itself, and is thus a self-contradiction.
- Explain the following sentence: the negation of a self-contradiction is a tautology.
The given sentence, “the negation of a self-contradiction is a tautology,” means that if we negate a self-contradiction, we get a statement that is always true, regardless of the truth value of its components, which is a tautology. This is because the negation of a self-contradiction asserts the opposite of the contradiction, which is always true, since the contradiction is inherently false. Therefore, the negation of a self-contradiction is always true, and hence a tautology.
- Explain the following sentence: the negation of a contingency is a contingency.
In logic and philosophy, a contingency refers to a proposition that is neither necessarily true nor necessarily false, but can be true or false depending on the circumstances or facts.
The negation of a contingency refers to the opposite of that proposition, which is either necessarily true or necessarily false, depending on the original proposition. For example, if the original proposition is “It may rain tomorrow,” the negation would be “It will not rain tomorrow.”
- What is it for two propositions to be consistent? What is it for them to be inconsistent?
Two propositions are considered consistent if it is possible for both of them to be true at the same time.
On the other hand, two propositions are considered inconsistent if they cannot both be true at the same time, meaning that they are contradictory.
- Define tautology.
In logic, a tautology is a statement that is true in every possible interpretation or situation. Put differently, a tautology is a proposition that is always true, regardless of the truth values of its individual components.
Example: either it will rain today or it will not
- Define contingency.
In logic, a contingency is a statement that is neither necessarily true nor necessarily false. In other words, a contingency is a statement that could be true or false, depending on the circumstances or context in which it is evaluated.
Example of a contingency is “I will pass my exam”, as the truth of the statement will depend on factors such as how well the person has studied, the difficulty of the exam, and the grading criteria.
- Show with a truth table that Disjunctive Syllogism is a valid rule of implication.
P Q P v Q ~P ~P -> Q
T T T F T
T F T F T
F T T T T
F F F T F
- Show with a truth table that Addition is a valid rule of implication.
P Q P v Q
T T T
T F T
F T T
F F F
- Give a natural language example of Exportation as a valid rule of replacement.
“if it snows this afternoon and we buy a sled, then we go sledding” is the same as saying “if it snows this afternoon, then if we buy a sled, then we go sledding”
- Show with a truth table that one of the DeMorgan’s Rules is a valid rule of replacement.
P Q ~(P * Q) (~P v ~Q)
T T F F
T F T T
F T T T
F F T T
- Show with a truth table that Transposition is a valid rule of replacement.
P Q ~P ~Q P -> Q ~Q -> ~P
T T F F T T
T F F T F F
F T T F T T
- Explain the following sentence: Commutation of conjunction does not respect temporal indexing with ‘and’.
In logic, Commutation of Conjunction is a valid rule of replacement that allows us to switch the order of two conjuncts in a conjunction. For example, if we have the statement “P and Q”, we can apply Commutation of Conjunction to obtain the equivalent statement “Q and P”.
However, when we use “and” as a temporal operator, the order of the conjuncts can have a different meaning depending on the context. For example, consider the following two statements:
“I will eat dinner and then watch a movie.”
“I will watch a movie and then eat dinner.”
In these statements, the order of the conjuncts is important because it specifies the temporal relationship between the events. Statement 1 implies that eating dinner will happen before watching a movie, while statement 2 implies the opposite.
Therefore, when “and” is used as a temporal operator, Commutation of Conjunction does not respect the temporal indexing, because switching the order of the conjuncts can change the meaning of the statement. This is why we must be careful when applying logical rules like Commutation of Conjunction in natural language contexts, especially when dealing with temporal relationships.
- What is the major operator rule for rules of implication?
The major operator rule for rules of implication is the rule that specifies that any rule of implication must preserve the truth value of the major operator in the original statement. In other words, if the major operator in the original statement is a conjunction, the rule of implication must preserve the truth value of the conjunction.
For example, consider the following statement:
“If it is raining and I don’t have an umbrella, then I will get wet.”
In this statement, the major operator is the conditional “if…then”. Any rule of implication that we apply to this statement must preserve the truth value of the conditional. For instance, we could apply the rule of Modus Ponens to infer the truth of the consequent:
“If it is raining and I don’t have an umbrella, then I will get wet.
It is raining and I don’t have an umbrella.
Therefore, I will get wet.”
In this argument, the rule of implication preserves the truth value of the conditional, which is the major operator in the original statement. This is the major operator rule for rules of implication.
- Explain how the Law of Non-Contradiction bears on the relationship between objects and classes in Categorical Logic.
Objects are individual entities that have specific attributes and exist in time and space. Classes, on the other hand, are groups or categories of objects that share common characteristics or attributes. The Law of Non-Contradiction asserts that an object cannot simultaneously belong to two classes that are mutually exclusive or contradictory. For example, a square cannot be both a polygon and a circle at the same time and in the same respect.
- Explain how the Law of Excluded Middles bears on the relationship between objects and classes in Categorical Logic.
In the context of objects and classes, the Law of Excluded Middle asserts that every object must either belong or not belong to a specific class. There is no middle ground or ambiguous state where an object might partially belong to a class. For example, a cat is either a member of the class of mammals or not. It cannot be partially a mammal and partially not a mammal.
- Explain what Existential Assumption is for Traditional Categorical Logic and why it is, for certain purposes, a
reasonable assumption.
existential assumption states that the only way to have a class is to have an object, and the only way to be an object is to exist
- What are the four standard forms in Categorical Logic?
A form: complete overlap, All S are P
E form: complete non-overlap, No S are P
I form: incomplete overlap, Some S are P
O form: incomplete non-overlap, Some S are not P
- Give an explanation with a Venn Diagram why “Only X are Y” should be translated in Standard form as “All
Y are X.” Provide an (intuitive) example.
only vandy grads are well-dressed = all well-dressed people are vandy grads
venn diagram with two circles crossed with v on left and w on right. have the w part shaded. then with an arrow pointing next to the diagram write all w are v.
- Give an explanation with a Venn Diagram why “The only X are Y” should be translated in Standard Form as
“All X are Y.” Provide an (intuitive) example.
the only millionaires at the party are vandy grads = all millionaires at the party are vandy grads
venn diagram m on left v on right with m section shaded.
- Explain with Venn Diagrams why A- and O- form propositions are contradictories.
x
- Explain with Venn Diagrams why E- and I- form propositions are contradictories.
x
- Explain with Venn Diagrams why E- and O- form propositions are subalterns.
x
- Explain with Venn Diagrams why A- and I- form propositions are subalterns.
x not totally sure
- Explain with Venn Diagrams why I- and O- form propositions are subcontraries.
x
- Explain with Venn Diagrams why A- and E- form propositions are contraries.
x
- Explain with Venn Diagrams why Conversion with A-Form Propositions is invalid. Provide an (intuitive)
counter-example.
x
- Explain with Venn Diagrams why Conversion with E-Form Propositions is valid. Provide an (intuitive)
example.
x
- Explain with Venn Diagrams why Contraposition with A-Form Propositions is valid. Provide an (intuitive)
example.
x