On a more mundane level, it is generally accepted that stealing is a violation of this moral law. Lewis argues that the moral law is like scientific laws (e.g. gravity) or mathematics in that it was not contrived by humans. However, it is unlike scientific laws in that it can be broken or ignored, and it is known intuitively, rather than through experimentation. After introducing the moral law, Lewis argues that thirst reflects the fact that people naturally need water, and there is no other substance which satisfies that need. Lewis points out that earthly experience does not satisfy the human craving for "joy" and that only God could fit the bill; humans cannot know to yearn for something if it does not exist.