 In addition, based on the logical equivalence  (NEC),  we can come to know “\(\Box A\)” by knowing “\(\neg A \boxarrow \bot\)”. And we know the latter through a counterfactual development of the antecedent of the counterfactual (“\(\neg A\)”), much like in the  (Rock)  example. If the counterfactual development of “\(\neg A\)” yields a contradiction (i.e., the consequent of the counterfactual in question), we assent to the counterfactual and thereby come to know that A is necessary. To take another example from Williamson: