Heidegger initiated a radical “thinking” – distinct from conventional forms of “philosophizing” – that cast doubt on the validity of the fundamental basis of Western philosophy. His approach questioned the authority of long-accepted notions of logic and truth by focusing its interrogation not on the content of existence, but on the “primary condition” that enables existence. Thus the most important and persistent view of Heidegger is as a pioneering thinker concerned first and foremost with investigating the significance of the primary condition for all life, which he called “Being”:

The ontological “error” of Western philosophy

Philosophical speculation on the nature of Being is known as ontology. It began in fifth-century bce Greece, when Presocratic thinkers such as Anaximander, Heraclitus and Parmenides became intrigued by the seemingly inexplicable fact of existence and introduced a new way of thinking about the world and the place of human beings in it.