You are coming back from a vacation. You want to go to village A. People from Village A always tell the truth, never lie. People from Village B always lie and never tell the truth. So, you come across two paths one leads to village A and the other leads to village B. You don't know which is which. A person comes from behind you. You don't know whether he is from village A or B. What can you ask him to choose the right path to village A?
"Can you point to the path which leads to the village you are from?" (If he is the truth teller and is from village A, he’ll point to village A. If he’s the liar from village B, he’ll lie and point to village A.)
What force from the sun keeps pulls on the earth and keeps it in orbit?