 First of all we need to be clear about what is meant by “necessity” here. What is at issue here is not logical necessity. It is rather inevitability. When the occurrence of a sea-battle on 1/1/2100 is said to be necessary at a certain date, what is meant is that at that date nothing can prevent a sea-battle from taking place on 1/1/2100. In particular, no one has the power to prevent it. Now Aristotle accepts that “What is, necessarily is, when it is; and what is not, necessarily is not, when it is not.” So, he accepts that, if a sea-battle is actually taking place on 1/1/2100, then on 1/1/2100 it is (in this sense) taking place of necessity. Nothing can then stop it happening, because it is happening. What this argument appears to establish, however, is that, if a sea-battle takes place on 1/1/2100, not only is it necessary then that a sea-battle takes place on 1/1/2100, but it was always necessary. No one could ever have prevented it. And the same applies to everything that can happen. So, in particular, no one ever has the power to do anything other that what they actually do.