Intentionality

Originally a concept from scholastic philosophy, intentionality was reintroduced in contemporary philosophy by the philosopher and psychologist Franz Brentano in his work Psychologie vom Empirischen Standpunkte. While often simplistically summarised as "aboutness" or the relationship between mental acts and the external world, Brentano defined it as one characteristic of "psychical phenomena" (psychische Phänomene), by which they could be distinguished from "physical phenomena" (physische Phänomene), using such phrases as "the relatedness to a content", the "direction towards an object", or "the immanent objectivity". Every psychical, or mental, phenomenon, 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. 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 psychical phenomena and physical phenomena, because physical phenomena lack intentionality altogether.

Through the works of Husserl, who took it over from Brentano, the concept of intentionality received more widespread attention in current philosophy, both continental and analytic. French philosopher Jean-Paul Sartre, in Being and Nothingness, identified intentionality with consciousness, stating that they were indistinguishable from one another, a position that was a stark contrast to Brentano's position that intentionality is but one quality of mental phenomena. German philosopher Martin Heidegger, in Being and Time, defined intentionality 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).

Other twentieth century philosophers such as Gilbert Ryle and Alfred Ayer have been critical of Husserl's concept of intentionality and his many layers of consciousness, Ryle insisting that perceiving is not a process and Ayer that describing one's knowledge is not to describe mental processes. The effect of these positions is that consciousness is so fully intentional that the mental act has been emptied of all content and the idea of pure consciousness is that it is nothing (Sartre also referred to "consciousness" as "nothing").

Platonist Roderick Chisholm has revived the Brentano thesis through linguistic analysis, distinguishing two parts to Brentano's concept, the ontological aspect and the psychological aspect. Chisholm's writings have attempted to summarize the suitable and unsuitable criteria of the concept since the Scholastics, arriving at a criteria of intentionality identified by the two aspects of Brentano's thesis and is defined by the logical properties that distinguish language describing psychological phenomena distinct from language describing non-psychological phenomena. Chisholm's criteria for the intentional use of sentences are: existence independence, truth-value indifference, and referential opacity.

In current artificial intelligence and philosophy of mind intentionality is a controversial subject and sometimes claimed to be something that a machine will never achieve. Explained in the chinese room thought experiment, the criticism is that while a computer may be able to say the word "tree", it will never be about an actual tree.

Other uses of the term
In the field of social cognition and the study of folk psychology, intentionality has a different meaning. Human perceivers consider a behavior intentional when it appears purposeful or done intentionally -- that is, based on reasons (beliefs, desires) and performed with skill and awareness. In many contexts, people read the intentions underlying others' behavior effortlessly.

N.B. intentionality (-tion-) is not to be confused with intensionality (-sion-), a concept from semantics.