In Philosophy of Science: An Encyclopedia, ed. J. Pfeifer and S. Sarkar (Routledge, forthcoming)


Some things are about, or are directed on, or represent, other things. For example, the sentence 'Cats are animals' is about cats (and about animals), this article is about intentionality, Emanuel Leutze's most famous painting is about Washington's crossing of the Delaware, lanterns hung in Boston's North Church were about the British, and a map of Boston is about Boston. In contrast, '#a$b', a blank slate, and the city of Boston are not about anything. Many mental states and events also have "aboutness": the belief that cats are animals is about cats, as is the fear of cats, the desire to have many cats, and seeing that the cats are on the mat. Arguably some mental states and events are not about anything: sensations, like pains and itches, are often held to be examples. Actions can also be about other things: hunting for the cat is about the cat, although tripping over the cat is not. This -- rather vaguely characterized -- phenomenon of "aboutness" is called intentionality. Something that is about (directed on, represents) something else is said to "have intentionality", or (in the case of mental states) is said to be an "intentional mental state".

This medieval terminology was reintroduced by the Austrian philosopher Franz Brentano in his 1874 book Psychology from an Empirical Standpoint (1995), although Brentano himself did not use the word 'intentionality'. (For a brief history of the terminology, and further references, see Crane 1998a; for an account of Brentano's thought, see Moran 2000, ch. 2. ) In a famous passage, Brentano claimed that every mental state/event has intentionality:

Every mental phenomenon is characterized by what the Scholastics of the Middle Ages called the intentional (or mental) inexistence of an object, and what we might call, though not wholly unambiguously, reference to a content, direction towards an object (which is not to be understood here as meaning a thing), or immanent objectivity. In presentation something is presented, in judgement something is affirmed or denied, in love loved, in hate hated, in desire desired, and so on. (1995, 88)

Brentano's use of 'intentional inexistence' is liable to confuse. Brentano did not mean that mental states are about peculiar nonexistent objects, but was rather referring to the (admittedly obscure) sense in which the object of a mental state is "in" the mind.

The terminology of 'intentionality' can also be confusing, for at least two reasons. First, intentionality has nothing in particular to do with intending, or intentions. Intentions, for instance the intention to buy a cat, are just one of many types of intentional mental states.

Second, intentionality (intentionality-with-a-t) must be sharply distinguished from intensionality (intensionality-with-an-s) (Searle 1983, ch. 1). Mental states are not intensional, only sentences are. A sentence s is intensional, or is an "intensional context", just in case substitution of some expression a in s with some coreferring expression b yields a sentence with different truth value from the truth value of s. So, for example, 'Necessarily, the number of planets is nine' and 'Hegel believed that the number of planets is seven' are intensional. Substituting 'nine' for the coreferential 'the number of planets' turns the first false sentence into the true sentence 'Necessarily, nine is nine', and the second true sentence into the false sentence 'Hegel believed that nine is seven'. As the first example indicates, a sentence can be intensional and yet have nothing to do with intentionality. Conversely, sentences that report intentional mental states/events need not be intensional (Crane 1998a). For example, 'Berkeley heard the coach' is (arguably) not intensional: if that sentence is true, and if 'the coach' and 'Locke's favorite carriage' refer to the same thing, then 'Berkeley heard Locke's favorite carriage' is true.

1. Paradoxes of intentionality

As informally explained above, an intentional mental state (for example) is "about" something. The belief that Brentano is Austrian is about Brentano. The object that the state is about is called the intentional object of the state. (Intentional objects are sometimes taken to include states of affairs as well as particulars like Brentanto: the belief that Brentano is Austrian could be said to be about Brentano's being Austrian.) So there should be a relation of "aboutness" that holds between a mental state and an object just in case the state is about the object -- "the intentional relation", in Brentano's terminology.

Thinking of intentionality in this way, as a relation to intentional objects, leads to three classic "paradoxes of intentionality" (Thau 2002, ch. 2). The first paradox is that the intentional object need not exist (at any time). The belief that the fountain of youth is in Florida bears the intentional relation to the fountain of youth, and the fountain of youth does not exist. But if a is related to b, then there is such a thing as a, and such a thing as b. One rather extreme solution, famously proposed by Brentano's student Alexius Meinong, is to hold that there are objects that do not exist. On this view, there is a fountain of youth, and the belief that the fountain of youth is in Florida bears the intentional relation to that (nonexistent) object. (This is Meinong's view, but not his terminology. Meinong used 'subsists' to mean exists, and 'exists' to mean something like spatiotemporally exists. Thus, in Meinong's terminology, Mont Blanc exists, the number 7 subsists but does not exist, and the fountain of youth neither exists nor subsists.)

The second paradox is that a mental state can bear the intentional relation to something, without there being any particular thing that the state bears the relation to. If one wants a cat, but has no particular cat in mind, then one's state of wanting a cat bears the intentional relation to an object -- a cat, presumably -- yet there is no particular cat that the state bears the intentional relation to. But if a is related to something, then there is a particular object that a is related to.

The third paradox is that a mental state can bear the intentional relation to a, but not bear the intentional relation to b, even though a is b. The belief that the first Postmaster General was a United States president is about the first Postmaster General, but not about the inventor of bifocals, even though the inventor of bifocals is the first Postmaster General, namely Benjamin Franklin. But if a bears a certain relation to b, and b= c, then a is related by the same relation to c.

In Psychology from an Empirical Standpoint Brentano himself did appear to think that a mental state was always related to an intentional object, but in a later appendix he insisted that the "only thing which is required by mental reference is the person thinking. The terminus of the so-called relation does not need to exist in reality at all" (1995, 272).

The moral of the paradoxes of intentionality is that thinking of intentionality in terms of "the intentional relation" is a bad idea. A better way involves drawing a distinction between the representational content of a mental state (or some other thing that has intentionality) and the objects (if any) the mental state is about. So, for example, the belief that the fountain of youth is in Florida has as its content the proposition that the fountain of youth is in Florida, and there is no object that the belief is about -- at any rate, not the fountain of youth (the belief is about Florida). To believe that the fountain of youth is in Florida is to stand in the belief-relation to the proposition that the fountain of youth is in Florida. This proposition exists whether or not the fountain of youth does (it does not contain the fountain of youth as a constituent), and this proposition is true just in case there is such a thing as the fountain of youth, and it is located in Florida. Similarly, the desire that one have a cat has as its content the proposition that one has a cat, and there is again nothing that the belief is about -- at any rate no particular cat. Finally, the belief that the first Postmaster General was a United States president and the belief that the inventor of bifocals was a United States President are both about the same object, namely Benjamin Franklin. However, there is some truth behind the original mistaken claim that the two beliefs are about different objects. This can be brought out by noting that the contents of the two beliefs are true at different possible worlds (of course, the contents are both false at the actual world). Specifically, the first proposition, but not the second, is true at a possible world in which the first Postmaster General became President and the inventor of bifocals never entered politics. The truth of the first proposition at a world depends on the political fortunes of whoever is the first Postmaster General at that world -- whether or not that individual invented bifocals.

2. Brentano's Two Theses

Brentano proposed two theses, summed up in the following passage, which form the basis of contemporary discussions of intentionality:

[I]ntentional in-existence is characteristic exclusively of mental phenomena. No physical phenomenon exhibits anything like it. We can, therefore, define mental phenomena by saying that they are those phenomena which contain an object intentionally within themselves. (1995, 89)

Brentano's first thesis is that no "physical phenomenon" has intentionality. Brentano's second thesis is that intentionality is the mark of the mental: all and only mental states/events have intentionality.

Brentano's examples of "physical phenomena" were not, say, brain processes, but were (chiefly) perceptible properties, like "color, sound and warmth" (1995, 92). Nonetheless, mainly through the influence of Roderick Chisholm, Brentano came to be associated with the doctrine that intentionality is not reducible to the physical -- in the contemporary sense of 'physical': see PHYSICALISM. Although quite dubious as an interpretation of Brentano (Moran 1996), it started a debate that continues to this day. Chisholm himself argued for the irreducibility of intentionality by first transforming this thesis into one about the sort of language adequate for psychology. Thus recast, the thesis of the irreducibility of intentionality becomes one about the ineliminability of intensional contexts, like 'Revere believes that the British are coming', in the language of a scientific psychology. (Chisholm called such sentences 'intentional sentences'.) Chisholm's reformulation of "a thesis resembling that of Brentano" is "that we do not need to use intentional language when we describe non-psychological phenomena; we can express all of our beliefs about what is merely 'physical' in sentences which are not intentional. But...when we wish to describe perceiving, assuming, believing, knowing, wanting, hoping, and other such attitudes, then either (a) we must use language which is intentional or (b) we must use terms we do not need to use when we describe nonpsychological phenomena" (1957, 172-3).

Chisholm argued for his "linguistic version" of Brentano's first thesis by arguing against various behavioristically-inspired analyses of "intentional language". Chisholm did not conclude that the failure of reduction impugned the reality of intentional mental states, but Quine famously did:

One may accept the Brentano thesis as either showing the indispensibility of intentional idioms and the importance of an autonomous science of intention, or as showing the baselessness of intentional idioms and the emptiness of a science of intention. My attitude, unlike Brentano's, is the second. (Quine 1960, 221)

Many philosophers are not so pessimistic, and there are many suggestions for providing a physicalistic or naturalistic reduction of intentionality. This is discussed in the following section.

Brentano's first thesis is true but has been (fruitfully) misinterpreted. Brentano's second thesis, on the other hand, has been correctly interpreted but seems obviously false, because of examples given in the first paragraph of this article. However, as discussed in the final section, Brentano's second thesis is in better shape than initial appearances suggest.

3. Reducing intentionality

Many philosophers hold that there must be a physicalistic/naturalistic reduction of intentionality -- at least, there must be if intentionality is a genuine phenomenon. Fodor is a prominent example:

I suppose that sooner or later the physicists will complete the catalogue they've been compiling of the ultimate and irreducible properties of things. When they do, the likes of spin, charm, and charge will perhaps appear on their list. But aboutness surely won't; intentionality simply doesn't go that deep...If the semantic and the intentional are real properties of things, it must be in virtue of their identity with (or maybe of their supervenience on?) properties that are themselves neither intentional nor semantic. If aboutness is real, it must be really something else. (Fodor 1987, 97)

There are many different approaches to providing the reduction of intentionality that Fodor says we need. Most adopt some kind of divide-and-conquer strategy. First, a distinction is made between original intentionality and derivative intentionality (Haugeland 1998; see also Searle 1992 for a similar distinction between intrinsic and derived intentionality). A thing has derivative intentionality just in case the fact that it represents such-and-such can be explained in terms of the intentionality of something else; otherwise it has original intentionality. Often the intentionality of language and other sorts of conventional signs is said to be derivative. Language, on this view, inherits its intentionality from the intentionality of mental states, specifically from the intentions and conventions adopted by language users (see Grice 1989, Part I). This is an attractive and plausible claim, although it is not obvious, and has been denied (see, for example, many of the essays in Davidson 1985). However, if it is correct, then the problem of reducing intentionality is itself reduced to the problem of reducing the intentionality of the mental.

Theories that attempt to provide a physicalistic reduction of intentionality fall into three broad groups. The first group comprises causal covariational theories (Stampe 1977, Dretske 1981, Stalnaker 1984, Fodor 1990). The basic idea is that mental states represent in much the same way that tree rings represent. The number of rings on a tree represents the tree's age, because the fact that the tree's age is n years old causes the tree to have n rings, or (a refinement) would cause the tree to have n rings in optimal conditions. A simple example of a causal covariational theory is this: a belief state S represents that p (that is, has propositional content that p) if and only if the fact that p would cause a subject to be in S. (This formulation takes the notion of a belief state for granted; a physicalistically acceptable version of the theory would have to provide a further reduction of a belief state.)

The second group comprises teleological theories (Papineau 1987, Millikan 1993, Dretske 1995). The basic idea is to explain the intentionality of mental states in terms of their biological functions, which might in turn be given a reductive account in terms of evolutionary history. A simple example is this: a belief state S represents that p if and only if in conditions in which a subject's cognitive system is functioning as it is designed to function by evolution, the subject would be in S when and only when it is the case that p.

The third group comprises functional role theories. Here the basic idea is that a representation or symbol means what it does because of its "functional role" -- its causal interaction with other representations. A simple example (for public language): a two-place sentence connective * means and if and only if the acceptance of sentence P and sentence Q is disposed to cause the acceptance of the sentence P^*^Q (i.e. P concatenated with * concatenated with Q), and the acceptance of P^*^Q is disposed to cause the acceptance of P and the acceptance of Q. If this is to be an account of thought rather than language, then there must be an appropriate range of neural representations -- perhaps words in a "language of thought". On "long-armed" functional role theories, functional roles are taken to include causal interactions with the environment (Harman 1999); "short-armed" functional role theories exclude such causal interactions, and for that reason are often taken to be accounts of the so-called "narrow content" of mental states (Block 1986).

Two other notable approaches should be mentioned. One is Dennett's "instrumentalism" (1987), which attempts to vindicate intentional notions from a physicalistic perspective without providing explicit reductions of the sort just illustrated. The other is Brandom's "inferentialism" (1994), which attempts to reduce intentionality to normativity, in particular to norms governing inferential practices.

4. Intentionality as the mark of the mental

Brentano's second thesis is independent of (the misinterpretation of) his first, that intentionality cannot be given a physicalistic reduction. The irreducibility of intentionality does not imply that all and only mental states/events are intentional. Searle is an example of a philosopher who holds that intentionality is irreducible, yet holds that sensations are not intentional. Neither does the converse implication hold: if intentionality is the mark of the mental, it might still be reducible. Tye and Dretske, whose views are explained below, think that intentionality is the mark of the mental, and that it can be given a physicalistic reduction.

Brenanto's second thesis divides into two parts: intentionality is sufficient for mentality and intentionality is necessary for mentality. The sufficiency claim is false -- at least if 'intentionality' is used in the broad and loose contemporary way, to include non-mental entities like sentences, paintings, and maps (see the beginning of this article). However, the sufficiency claim might be amended as follows: original intentionality is sufficient for mentality. According to the revised sufficiency claim, the mental is the source of all intentionality. This revised claim still faces problems. First, if the indication of a tree's age by the number of its rings is an example of intentionality at all, then it is presumably original intentionality. And if it is original intentionality, the sufficiency claim is false. Again, the sufficiency claim is false if the intentionality of language does not derive from the intentionality of the mental. But these are controversial issues, and there is at least some prospect of defending a modified version of Brentano's sufficiency claim.

Matters might seem even less promising with the other part of Brentano's second thesis, the claim that intentionality is necessary for mentality. At any rate, some philosophers think that sensations are obviously non-intentional. However, the claim that bodily sensation is a form of perception of one's own body was defended in the 1960's by D. M. Armstrong (1968) and has been revived today by a number of philosophers including Dreske (1995), Lycan (1996), and Tye (1995). And if this thesis is correct, then because perceptions have intentionality, bodily sensations are not counterexamples to the claim that intentionality is necessary for mentality. (For Brentano's own account of the intentionality of pain, which anticipates many modern discussions, see 1995, 82-5.)

More problematic cases are provided by certain "objectless" emotions, like forms of anxiety or depression where one is hard put to say what one is anxious or depressed about (Searle 1983, ch. 1). For defenses of Brentano's second thesis against this sort of example, see Tye 1995, 128-31, and Crane 1998b.

Assuming that every mental state/event is intentional, a further issue arises, whether the representational content of a mental state determines "what it's like" to be in the state -- the state's "qualia". Dretske, Lycan, and Tye, among others, endorse this determination claim. Such an "intentional theory of qualia" is controversial, and has been widely discussed in the literature on consciousness.


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Alex Byrne
Massachussetts Institute of Technology