Intentionality

# Overview
The term intentionality is often simplistically summarized as "aboutness" or the relationship between mental acts and the external world. Originally intentionality was a concept from scholastic philosophy. The concept of intentionality 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 intentionality as one characteristic of "mental phenomena," by which they could be distinguished from "physical phenomena" (physische Phanomene), 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 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).

# Modern views
Other twentieth century philosophers such as Gilbert Ryle and A J 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 criterion of intentionality identified by the two aspects of Brentano's thesis and defined by the logical properties that distinguish language describing psychological phenomena 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. John Searle argued for this position with the Chinese room thought experiment, according to which no syntactic operations that occurred in a computer would provide it with semantic content. As he noted in the article, Searle's view was a minority position in artificial intelligence and philosophy of mind.
Daniel Dennett offers a taxonomy of the current theories of intentionality in Chapter 10 of his book "The Intentional Stance". Most, if not all, current theories on intentionality accept Brentano's thesis of the irreducibility of intentional idiom. From this thesis two positions emerge: (1) that intentional idiom is problematic for science and (2) that intentional idiom is not problematic for science. Chisholm (1956), Anscombe (1957), Geach (1957), and Taylor (1964) all adhere to the former position, namely that intentional idiom is problematic and cannot be integrated with the natural sciences. Members of this category also maintain realism in regard to intentional objects, which may imply some kind of dualism (though this is debatable).
The latter position, which maintains the unity of intentionality with the natural sciences, is further divided into three standpoints: (A) Eliminative Materialism, supported by W.V. Quine (1960) and Churchland (1981), (B) Realism, advocated by Jerry Fodor (1975), as well as Burge, Dretske, Kripke, and the early Hilary Putnam, and (C) those who adhere to the Quinean Double Standard. Proponents of A, the eliminative materialists, understand intentional idiom, such as "belief", "desire", and the like, to be replaceable either with behavioristic language (e.g. Quine) or with the language of neuroscience (e.g. Churchland). Holders of B, the realists, argue, in contrast to those in support of C, that there is a deeper fact of the matter to both translation and belief attribution. In other words, manuals for translating one language into another cannot be set up in different yet behaviorally identical ways and ontologically there are intentional objects. Famously, Fodor has attempted to ground such realist claims about intentionality in a language of thought. Dennett comments on this issue, Fodor "attempt to make these irreducible realities acceptable to the physical sciences by grounding them (somehow) in the 'syntax' of a system of physically realized mental representations" (Dennett 1987, 345).
Those who adhere to position C, the Quinean double standard (namely that ontologically there is nothing intentional, but that the language of intentionality is indispensable), accept Quine's thesis of the indeterminacy of radical translation and its implications, while the other positions so far mentioned do not. As Quine puts it, indeterminacy of radical translation is the thesis that "manuals for translating one language into another can be set up in divergent ways, all compatible with the totality of speech dispositions, yet incompatible with one another" (Quine 1960, 27). Quine (1960) and Wilfrid Sellars (1958) both comment on this intermediary position. One such implication would be that there is, in principle, no deeper fact of the matter that could settle two interpretative strategies on what belief to attribute to a physical system. In other words, the behavior (including speech dispositions) of any physical system, in theory, could be interpreted by two different predictive strategies and both would be equally warranted in their belief attribution. This category can be seen to be a medial position between the realists and the eliminativists since it attempts to blend attributes of both into a theory of intentionality. Dennett, for example, argues in "True Believers" (1981) that intentional idiom (or "folk psychology") is a predictive strategy and if such a strategy successfully and voluminously predicts the actions of a physical system, then that physical system can be said to have those beliefs attributed to it. Dennett calls this predictive strategy the intentional stance.
Position C is further divided into two: (i) adherence to the Normative Principle and (ii) adherence to the Projective Principle. The latter is advocated by Grandy (1973) and Stich (1980, 1981, 1983, 1984), who maintain that attributions of intentional idioms to any physical system (e.g. humans, artifacts, non-human animals, etc.) should be the propositional attitude (e.g. "belief", "desire", etc.) that one would suppose one would have in the same circumstances (Dennett 1987, 343).
Advocates of the former, the Normative Principle, argue that attributions of intentional idioms to physical systems should be the propositional attitudes that the physical system ought to have in those circumstances (Dennett 1987, 342). However, exponents of this view are still further divided into those who make an Assumption of Rationality and those who adhere to the Principle of Charity. Dennett (1969, 1971, 1975), Cherniak (1981, 1986), and the late Putnam (1983) recommend the Assumption of Rationality, which unsurprisingly assumes that the physical system in question is rational. Donald Davidson (1967, 1973, 1974, 1985) and Lewis (1974) defend the Principle of Charity.

# Intentionality vs. intensionality
Intentionality should not be confused with intensionality, a concept from semantics though it is related to the modern understanding of intention.