The philosopher king is a hypothetical ruler in whom political skill is combined with philosophical knowledge. The concept of a city-state ruled by philosophers is first explored in Plato's Republic, written around 375 BC. Plato argued that the ideal state – one which ensured the maximum possible happiness for all its citizens – could only be brought into being by a ruler possessed of absolute knowledge, obtained through philosophical study. From the Middle Ages onwards, Islamic and Jewish authors expanded on the theory, adapting it to suit their own conceptions of the perfect ruler. Several historical figures, including Alexander the Great and Marcus Aurelius, have been described by ancient and modern writers as embodying the philosopher king ideal. In the Republic The Republic is a Socratic dialogue. In the first two books, Socrates is challenged to give a definition of justice, which he proposes to accomplish by imagining how an ideal city-state would function. He suggests that the ideal state would be ruled over by a specially trained Guardian class, in whom a spirited nature would be combined with a philosophic disposition. Socrates goes on to discuss various aspects of life within the state. In the fifth book, Socrates' interlocutors ask him whether the state he is describing could ever exist in reality. He replies that this could only happen on one condition: Socrates clarifies this comment by distinguishing between true and false philosophers. The true philosopher (or "lover of wisdom") is one who loves "the truth in each thing", as opposed to those who only love the things themselves. This is a reference to Plato's belief that all particular things are only shadows of eternal Forms. Only the philosopher, therefore, is qualified to rule, as only the philosopher has knowledge of the absolute truth, and is able to apply this knowledge for the good of the state. Socrates next outlines the qualities which the ideal philosopher must possess, including truthfulness, temperance, justice, and a good memory. It is observed, however, that this ideal is in sharp contrast to reality, as many philosophers are "utter rogues", and the best of them are generally considered to be useless. Socrates explains the poor reputation of philosophers through the metaphor of the Ship of State, in which he compares Athenian democracy to a group of mutinous sailors vying with one another for control of the helm of a ship. The sailors, having themselves