 Another issue concerned identifying the contradictory of a proposition containing a relative. A categorical containing a relative of identity such as ‘A, which is B, is C’ is equivalent to ‘A is B and A is C’. Hence its contradictory, ‘A, which is B, is not C’, says Albert of Saxony, is equivalent to ‘A is not B or A is not C’: “The second rule: a negative categorical proposition in which a relative term occurs is equivalent to a disjunctive proposition: e.g., ‘Socrates, who is running, is not disputing’ has the same truth-value as ‘Socrates is not running or Socrates is not disputing’. And therefore such a proposition has two causes of truth, each of which is sufficient on its own for its truth. Hence ‘Socrates, who is running, is not disputing’ is true either because Socrates is not running or because Socrates is not disputing. Hence because by the first rule the affirmative is equivalent to a conjunction, it follows that the negative contradictory to it is equivalent to a disjunction composed from the contradictories of the conjuncts, since conjunctions and disjunctions with contradictory parts contradict one  another”.[40]