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LSAT Conditional Reasoning and Diagramming

Translating LSAT conditional statement language (unless, only if, no...without) into formal logic diagrams, a practice-focused companion to the logic terminology deck.

32 cards · basic cards · AI-written, checked twice. Edit anything.

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What does 'If A then B' mean in logical terms?
If A is true, then B must be true. A is sufficient for B.
What is the contrapositive of 'If A then B'?
If not B, then not A. The contrapositive is logically equivalent to the original.
What is a sufficient condition?
A condition that guarantees a result. If A is sufficient for B, then whenever A is true, B must be true.
What is a necessary condition?
A condition required for something to happen. If B is necessary for A, then A cannot occur unless B occurs.
In the diagram 'A → B', what does the arrow represent?
A conditional: if A then B. A is sufficient for B and B is necessary for A.
Translate 'Unless A, B' into a conditional statement.
If not A, then B. Equivalently, either A or B (or both) must be true.
Why is 'Unless A, B' logically equivalent to 'A or B'?
Because at least one must be true: either A happens, or (if A does not) then B must happen.
Translate 'B is not true unless A is true' into a conditional.
If B then A. B is sufficient for A and A is necessary for B.
What does 'A only if B' mean?
B is necessary for A. If A happens, then B must happen. Diagram: A → B.
What is the difference between 'If A then B' and 'A if B'?
'If A then B' is A → B. 'A if B' is B → A (B is sufficient for A).
Translate 'No A without B' into a conditional.
If A, then B. A cannot occur without B occurring.
Translate 'All A are B' into a conditional.
If A, then B. Every member of A is also a member of B.
Translate 'No A are B' into a conditional.
If A, then not B. Nothing that is A can be B.
What is the contrapositive of 'No A are B'?
If B, then not A.
What does 'Neither A nor B' mean?
Not A and not B. Both A and B must be false.

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