Plato's Sophist is a dialogue between Socrates and two other philosophers, Theaetetus and an unnamed Stranger. The three engage in a philosophical discussion about the nature of being and the art of sophistry. The Stranger argues that there are two types of beings: those that are visible and tangible, such as physical objects, and those that are invisible and intangible, such as ideas and concepts. The Stranger claims that the art of sophistry is the manipulation of these intangible beings, which he calls "non-being."