The book explicitly requires appropriate modal opposition in the contradiction of modal propositions. Necessity, possibility and permanence qualify a claim differently.
For example:
“Every human is necessarily a writer.”
“No human is necessarily a writer.”
These do not automatically form a contradictory pair: both may be false. Simply reversing affirmation and negation while leaving modal scope unexamined is insufficient.
A correct modal contradictory must negate the full modal assertion.
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Contradiction: Definition, Conditions and Application to Propositions
The book explicitly requires appropriate modal opposition in the contradiction of modal propositions. Necessity, possibility and permanence qualify a claim differently.
For example:
“Every human is necessarily a writer.”
“No human is necessarily a writer.”
These do not automatically form a contradictory pair: both may be false. Simply reversing affirmation and negation while leaving modal scope unexamined is insufficient.
A correct modal contradictory must negate the full modal assertion.