Logical Connectives - Beginner Level: truth tables BEGINNER

Step 1: Understand 'unless' statements
'P unless Q' means 'If not Q, then P'
In logical form: 'P unless Q' ≡ '¬Q → P'

Step 2: Identify components
Original: She won't come unless you invite her
p: She won't come, q: You invite her

Step 3: Convert to if-then form
'unless' tells us what happens if the condition is NOT met
Logical form: ¬q → p

Step 4: Write in English
Equivalent statement: If you do not invite her, then she won't come

Step 1: Understand what logical equivalence means
Two expressions are logically equivalent if they have the same truth value for ALL possible combinations of variables.

Step 2: Analyze the expressions
Expression 1: p → q
Expression 2: q → p

Step 3: Test with truth table
p → q (implication) is NOT the same as q → p (converse).
Counter-example: p=F, q=T
p → q = F → T = T
q → p = T → F = F
Since they differ, they are NOT equivalent.

Rule: Conjunction Introduction (∧-intro)

If you have P and you have Q, you can combine them into P ∧ Q.

Answer: p ∧ q

Step 1: Break down the compound expression
Expression: ¬(p ∧ q)

Step 2: Evaluate inner expression first
p ∧ q = False ∧ False = False

Step 3: Apply negation
¬(False) = True
Negation reverses the truth value

Step 1: Understand the original statement
Original: p → q means "If it is raining, then the ground is wet"

Step 2: Understand Inverse
Inverse negates both parts: ¬p → ¬q
If the original is p → q, the inverse is ¬p → ¬q

Step 3: Apply to our statement
Inverse: If it is raining is false, then the ground is wet is false

Step 1: Understand 'only if' statements
'P only if Q' means 'If P, then Q' (P → Q)
This is DIFFERENT from 'If Q then P' (Q → P)

Key insight: 'only if' introduces a NECESSARY condition
Q is necessary for P (P cannot be true without Q)

Step 2: Identify components
Statement: You will pass only if you study
P: You pass, S: You study

Step 3: Convert to logical form
Logical form: P → S
Equivalent: If you pass, then you studied

Step 4: Important distinction
Note: Studying is necessary but not sufficient
'Only if' ≠ 'If and only if'
'Only if' gives one direction only (→)
'If and only if' gives both directions (↔)

Step 1: Understand the conjunction (AND) operator
The conjunction p ∧ q is True ONLY when BOTH p and q are True.

Step 2: Apply the given values
p = False, q = False

Step 3: Evaluate p ∧ q
Since at least one of p or q is False, p ∧ q = False

Step 1: Understand the original statement
Original: p → q means "If the alarm rings, then I wake up"

Step 2: Understand Converse
Converse switches the hypothesis and conclusion: q → p
If the original is p → q, the converse is q → p

Step 3: Apply to our statement
Converse: If I wake up, then the alarm rings

Step 1: Understand necessary and sufficient conditions
• P is NECESSARY for Q: Q cannot be true without P (Q → P)
• P is SUFFICIENT for Q: P being true guarantees Q (P → Q)
• P is BOTH: P if and only if Q (P ↔ Q)

Step 2: Analyze the relationship
P: Being a square
Q: Being a rectangle

Step 3: Determine the condition type
All squares are rectangles (sufficient), but not all rectangles are squares (not necessary)

Answer: Sufficient but not necessary

Step 1: Understand necessary and sufficient conditions
• P is NECESSARY for Q: Q cannot be true without P (Q → P)
• P is SUFFICIENT for Q: P being true guarantees Q (P → Q)
• P is BOTH: P if and only if Q (P ↔ Q)

Step 2: Analyze the relationship
P: Being a triangle
Q: Having three sides

Step 3: Determine the condition type
A shape is a triangle if and only if it has three sides

Answer: Necessary and sufficient

Step 1: Understand necessary and sufficient conditions
• P is NECESSARY for Q: Q cannot be true without P (Q → P)
• P is SUFFICIENT for Q: P being true guarantees Q (P → Q)
• P is BOTH: P if and only if Q (P ↔ Q)

Step 2: Analyze the relationship
P: Being a square
Q: Being a rectangle

Step 3: Determine the condition type
All squares are rectangles (sufficient), but not all rectangles are squares (not necessary)

Answer: Sufficient but not necessary

Step 1: Understand Exclusive OR (XOR)
Exclusive OR (p ⊕ q) is True when EXACTLY ONE of p or q is True.
It is False when both are True or both are False.

Truth table for p ⊕ q:
p=T, q=T → Result=F (both true)
p=T, q=F → Result=T (exactly one)
p=F, q=T → Result=T (exactly one)
p=F, q=F → Result=F (neither true)

Step 2: Apply the given values
p = False, q = True

Step 3: Evaluate the exclusive OR
Since exactly one of p or q is True, the exclusive OR is True

'Neither P nor Q' means ¬P ∧ ¬Q (both are false).

Answer: ¬j ∧ ¬m

Step 1: Understand the conjunction (AND) operator
The conjunction p ∧ q is True ONLY when BOTH p and q are True.

Step 2: Apply the given values
p = True, q = True

Step 3: Evaluate p ∧ q
Since both p and q are True, p ∧ q = True

'If P then Q' translates to P → Q (implication).

Answer: p → q

Step 1: Understand necessary and sufficient conditions
• P is NECESSARY for Q: Q cannot be true without P (Q → P)
• P is SUFFICIENT for Q: P being true guarantees Q (P → Q)
• P is BOTH: P if and only if Q (P ↔ Q)

Step 2: Analyze the relationship
P: Being divisible by 4
Q: Being an even number

Step 3: Determine the condition type
All numbers divisible by 4 are even (sufficient), but not all even numbers are divisible by 4 (not necessary)

Answer: Sufficient but not necessary

Step 1: Break down the compound expression
Expression: p → (q ∧ r)

Step 2: Evaluate inner expression first
q ∧ r = True ∧ False = False

Step 3: Evaluate outer expression
p → (False) = True → False = False
Implication is False only when antecedent is True and consequent is False

Step 1: Understand the disjunction (OR) operator
The disjunction p ∨ q is True when AT LEAST ONE of p or q is True.
It is False ONLY when both p and q are False.

Step 2: Apply the given values
p = False, q = True

Step 3: Evaluate p ∨ q
Since at least one of p or q is True, p ∨ q = True

Step 1: Break down the expression
Expression: ¬p ∨ (q ∧ r)
Given: p=F, q=T, r=T

Step 2: Evaluate inner expressions first
¬p = T
q ∧ r = T ∧ T = T

Step 3: Evaluate outer expression
T ∨ T = True
Remember: OR is True when at least one operand is True

Step 1: Break down the compound expression
Expression: ¬(p ∧ q)

Step 2: Evaluate inner expression first
p ∧ q = True ∧ False = False

Step 3: Apply negation
¬(False) = True
Negation reverses the truth value