Confusing Sufficiency for Necessity

A → B

_

B → A

Denying the Sufficient Condition

A → B

/A

_

/B

Affirming the Necessary Condition

A → B

B

A

Most Statements are Not Reversible

A —m→ B

_

B —m→ A

All Before Most

A → B —m→ C

_

A ←s→ C

All Before Some

A → B ←s→ C

_

A ←s→ C

Most Before Most

A —m→ B —m→ C

A ←s→ C

Some Before Some

A ←s→ B ←s→ C

A ←s→ C