Until recently I thought the trickiest thing about long-term intergenerational ethics was the need to peer into distant, largely unpredictable futures. I have changed my mind. After pondering sentences like ‘Unborn generations depend on us’ (will depend? are going to depend? will be already depending? are yet going to have used to depend? will have been using to go to be having depended?) I’m just glad I don’t also have to deal with the grammar of time travel.