And if you took Natural Selection to Ahead Four “I know,” he said without looking up. “You were wise to keep the entire ship in deep-sea state.” “It had to be this way. Otherwise, agitated officers and soldiers would have attacked this cabin. _And if you took Natural Selection to Ahead Four at will, you would have killed them all_. That’s also the reason why the pursuers haven’t closed in.” Excerpt From The Dark Forest (Remembrance of Earth's Past) Cixin Liu Context: the ship called “Natural Selection” is a extremely large spaceship. There are four types of acceleration among which the highest is called “The Ahead Four”, which would allow the spaceship to travel at one-hundredth the speed of light. According to physics, the passengers (in this case, the officers and soldiers) would be dead in a spaceship traveling that fast—only deep-sea state can protect them. And before the quoted conversation, the spaceship has already been taken to Ahead Four. Question: Why is “if you took” instead of “if you had taken” used here? Thank you.