In particular hermeneutics is a method for interpreting texts, but more generally the word refers to the art, skill, theory and philosophy of interpretation and understanding. Contemporary hermeneutics is partly derived from 19th century German historians such as Dilthey, where a central issue was the distinction between natural and social phenomena, and hence the natural and social sciences, with their different modes of acquiring knowledge, ie understanding (verstehen) versus explanation (erklaren). It was given a new basis through phenomenology by Heidegger, who saw understanding as constitutive of human existence, and thus a phenomenology of human existence is a phenomenology of understanding. Of importance here is Heidegger’s concept of pre-understanding, which Gadamer took up in connection with the notions of prejudice, tradition and authority which are of central importance to contemporary hermeneutics, and constitute the basis of the hermeneutic spiral.