Philosophers have provided many perspectives. An influential ancient view was that of the Republic in which Plato explored the question "what is justice?" and postulated that it is not primarily a matter among individuals but of society as a whole, prompting him to devise a utopia . Two thousand years later René Descartes declared " I think, therefore I am " because he believed the human mind, particularly its faculty of reason , to be the primary determiner of truth ; for this he is often credited as the father of modern philosophy.  One such modern school, existentialism , attempts to reconcile an individual's sense of disorientation and confusion in a universe believed to be absurd .