intentionality aboutness. Things that are about other things exhibit intentionality. Beliefs and other mental states exhibit intentionality, but so, in a derived way, do sentences and books, maps and pictures, and other representations. The adjective ‘intentional’ in this philosophical sense is a technical term not to be confused with the more familiar sense, characterizing something done on purpose. Hopes and fears, for instance, are not things we do, not intentional acts in the latter, familiar sense, but they are intentional phenomena in the technical sense: hopes and fears are about various things.
The term was coined by the Scholastics in the Middle Ages, and derives from the Latin verb intendo, ‘to point (at)’ or ‘aim (at)’ or ‘extend (toward)’. Phenomena with intentionality thus point outside of themselves to something else: whatever they are of or about. The term was revived by the nineteenth-century philosopher and psychologist Franz Brentano, who claimed that intentionality defines the distinction between the mental and the physical; all and only mental phenomena exhibit intentionality. Since intentionality is an irreducible feature of mental phenomena, and since no physical phenomena could exhibit it, mental phenomena could not be a species of physical phenomena. This claim, often called the Brentano thesis or Brentano’s irreducibility thesis, has often been cited to support the view that the mind cannot be the brain, but this is by no means generally accepted today. There was a second revival of the term in the 1960s and 1970s by analytic philosophers, in particular Chisholm, Sellars, and Quine. Chisholm attempted to clarify the concept by shifting to a logical definition of intentional idioms, the terms used to speak of mental states and events, rather than attempting to define the intentionality of the states and events themselves. Intentional idioms include the familiar ‘mentalistic’ terms of folk psychology, but also their technical counterparts in theories and discussions in cognitive science, ‘X believes that p,’ and ‘X desires that q’ are paradigmatic intentional idioms, but according to Chisholm’s logical definition, in terms of referential opacity (the failure of substitutivity of coextensive terms salva veritate), so are such less familiar idioms as ‘X stores the information that p’ and ‘X gives high priority to achieving the state of affairs that q’. Although there continue to be deep divisions among philosophers about the proper definition or treatment of the concept of intentionality, there is fairly widespread agreement that it marks a feature – aboutness or content – that is central to mental phenomena, and hence a central, and difficult, problem that any theory of mind must solve. See also BRENTANO, FOLK PSYCHOLOGY , QUANTIFYING IN , REFERENTIALLY TRANSPAR — EN. D.C.D.