|Geach, Peter T.
Books on Amazon
Contradictions/Sentence/Geach: Contradictions of sentences can only be achieved through the negation of predicates, never by the negation of a name
Contradiction: no sentence can have two (non-equivalent) contradictions - contrary: one sentence may have several contradictory sentences (assertions) - contradiction only through negation of predicate, never of subject - contradictions: ditto
Logic Matters Oxford 1972