Mark Twain once went to borrow a book from a neighbour in Tarrytown.
"May I borrow a book from you?" he asked politely.
"Yes, you're more than welcome to it," the neighbour replied. "But I must ask you to read it here. You know I make a rule never to let any book leave my library."
Some days later, the neighbour wished to borrow Twain's lawn mower.
"Why, certainly," Twain told him. "You're more than welcome to it. But I must ask you to use it here. You know I make it a rule never to let it leave my garden."