The term<unk>  is often simplistically summarized as "aboutness" or the relationship between mental acts and the external world. Originally<unk>  was a concept from scholastic philosophy. The concept of<unk>  was later reintroduced in 19th century contemporary philosophy by the philosopher and psychologist Franz Brentano in his work Psychology from an Empirical Standpoint (1874). Brentano defined<unk>  as one characteristic of "mental phenomena," by which they could be distinguished from "physical phenomena" (physische Phänomene), using such phrases as "reference to a content", the "direction towards an object", or "the immanent objectivity".
Every mental phenomenon (that is, every psychological act) has a content, and is directed at an object (the intentional object). Every belief, desire, etc. has an object that it is about: the believed, the wanted, etc.. Brentano used the expression "intentional inexistence" to indicate the status of the objects of thought in the mind. The property of being intentional, of having an intentional object, was the key feature to distinguish mental phenomena and physical phenomena, because physical phenomena lack<unk>  altogether.
Through the works of Husserl, who took it over from Brentano, the concept of<unk>  received more widespread attention in current philosophy, both continental and analytic. French philosopher Jean-Paul Sartre, in Being and Nothingness, identified<unk>  with consciousness, stating that they were indistinguishable from one another, a position that was a stark contrast to Brentano's position that<unk>  is but one quality of mental phenomena. German philosopher Martin Heidegger, in Being and Time, defined<unk>  as "care" (Sorge), a sentient condition where an individual's existentiality, facticity, and forfeiture to the world identifies their ontological significance, in contrast to that which is the mere ontic (thinghood).
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