Every summer my husband and I pack our suitcases, load our kids into the car, and drive from tense, crowded New York City to my family's cottage in Maine. It's on an island, with stretches of sea and sandy beaches, rocky coasts, and pine trees. We barbecue, swim, lie around, and try to do nothing.
Finally there are simple ideas of which no definition can be given; there are also axioms or postulates, or in a word primary principles, which cannot be proved and have no need of proof.