<p>There are two reasons why it’s more logical for you to be required to put the seat up than for her to be required to put the seat down. </p>
<p>The first is simply that the seat is down by default. Whenever you buy or close a toilet, the seat is down. You have to make the effort to put the seat up, so you should put it back down. She shouldn’t have to put it down and then back up, since the default state is for the seat to be down.</p>
<p>The second reason is utilitarian: it makes everyone better off if the seat is left down after every use. You can go number one whether the seat is down or up, though obviously the latter is somewhat more convenient. She cannot go number one if the seat is up, only if it’s down. So it’s logical that you should leave the seat down. This way, when one of you forgets to move the seat, there’s not a problem.</p>