 He then produces an argument to show (what most of us believe) that either it is not in my power to read a headline saying that there was a sea-battle yesterday or it is not in my power to read a headline saying that there was no sea-battle yesterday, at any rate if we make some obvious assumptions about the relation between the headlines and what took place. Letting S be the act of reading a headline that there was a sea-battle, and S′ be the act of reading a headline that there was no sea-battle; and letting P and P′ be the propositions that there was and was not such a battle, the argument goes: