Piero Scaruffi(Copyright © 2006 Piero Scaruffi | Legal restrictions - Termini d'uso )
Meaning: A Journey to the Center of the Mind
(These are excerpts from, or extensions to, the material published in my book "The Nature of Consciousness")
The Meaning of Meaning: knowing what things are
Meaning is intuitively very important. We all assume that what matters is the meaning of something, not the something per se. But then nobody really knows how to define what "meaning" means. The symbol "LIFE" per se is not very interesting, but the thing it means is very interesting.
Before we can answer the question "what is the meaning of life?" we need to answer to the simpler question: "what is meaning?" What do we mean when we say that something means something else?
Linguistic principles are innate and universal. Everybody is born with the ability to learn language. But our language ability depends not only on symbolic utterance (on constructing grammatically-correct sentences), but also on our ability to make use of symbolic utterance, to connect the idea with some action. Spoken language is not even that essential: we can communicate with gestures and images. This happens since birth, as linguistic and nonlinguistic information (e.g., visual) are tied from the beginning. What matters is the ability to comprehend. As a matter of fact, in a baby comprehension is ahead of utterance.
Since meaning is first and foremost "about" something, an obvious component of meaning is what philosophers call "intentionality": the ability to refer to something else. The word "LIFE" refers to the phenomenon of life. Far from being an exclusive of the human mind, meaning in this broad sense is rather pervasive in nature. One could even claim that everything in nature refers to everything else, as it would probably not exist without the rest of the universe. Certainly, a shadow refers to the object that makes it, and a crater refers to the meteor that created it. But "meaning" in the human mind also involves being aware of it, and in this narrow sense "meaning" could be an exclusive of the human mind. There are, therefore, at least two components of meaning: intentionality and awareness. Something refers to something else, and I am aware of this being the case.
At the same time meaning affects two complementary aspects of our mind: language (i.e., the way we communicate meaning to other thinking beings) and concepts (i.e., the way we store meaning for future reference). As the British philosopher Paul Grice noted, there are two different meanings to the word "meaning": "what did she mean" and "what does that refer to". The meaning of a speaker is what she intended to say. There is an intention to take into account. The meaning of a word relating to a natural phenomenon is what it refers to (the meaning of "LIFE" is the phenomenon of life).
There is another dimension to meaning. Think of water, a fairly innocent subject: what does the concept of "water" refer to? The substance? The chemical compound H2O? Something liquid and transparent that is found in rivers and in the rain? Imagine that in another world there is a substance that looks and behaves just like water, but is made of a different chemical compound. When I and a person of that world think of water, are we referring to the same thing or to two different things? What is a clock? An object whose function is that of marking the time (which could be a sundial)? Or an object whose structure is round, has two hands and 12 numbers (which could be a toy clock that does not perform any actual function)?
Intension and Extension: what is a concept?
A fundamental step in the discussion of meaning was Gottlob Frege's distinction between "sense" and "reference", which led to the distinction between "intension" and "extension". The "referent" of a word is the object it refers to, the "sense" of that word is the way the referent is given. For example, "the star of the morning" and "the star of the evening" have two different senses but the same referent (they both refer to the planet Venus). A more important example: propositions of classical Logic can only have one of two referents, true or false.
The "extension" of a concept is all the things that belong to that concept. For example, the extension of "true" is the set of all the propositions that are true. The "intension" of that concept is the concept itself. For example, the extension of "red" is all the objects that are red, whereas the intension of "red" is the fact of being red. There is an intuitive relationship between sense and intension, and between reference and extension.
But the relationship between sense and reference is not intuitive at all, as proved by the difficulty in handling indexicals (words such as "I") and demonstratives (such as "this"). The proposition "I am Piero Scaruffi" is true or false depending on who utters it. The proposition "I am right and you are wrong" has two completely opposite meanings depending on who utters it.
A number of alternatives to Frege’s analysis have been proposed over the decades: Saul Kripke's and Hilary Putnam's "causal theory of reference" (which assumes a causal link between a word and what it stands for); Kripke's distinction of "rigid designators" and "non-rigid designators" in the context of possible worlds; and Richard Montague's intensional-logic approach (in which the sense of an expression is supposed to determine its reference). These are all different views on how sense and reference relate.
Meaning is what we do with it
Ludwig Wittgenstein introduced a different way of thinking about meaning, a common-sense way that identifies meaning with use. The meaning of something is what we do with it. This led to Conceptual/functional/inferential/procedural role semantics.
Similarly, proof-theoretic semantics, spearheaded in the 1940s by the German mathematician Gerhard Gentzen, takes the meaning of a propositions to be defined by the role that the proposition plays within the system of inference.
Does meaning exist?
"Nominalism" is a centuries-old philosophical faith according to which "universals" exist only in our mind and language. We tend to assign them a reality of their own when, in reality, they are just conventions used by our minds and our language.
At the other end of the spectrum, Plato claimed that ideas exist in a world of their own, independent of our material world.
What is a theory of truth? Let's take an example from Physics, a science that is famous for theories. A theory of electricity is an explanation of the nature and cause of electricity and a set of laws that electrical phenomena obey. A theory of truth is essentially an explanation of the nature of truth and a set of laws that "true" things obey.
Electricity is the property that all electrical things share. What is the property that all true statements have in common?
Why is a theory of truth important? Because that is what, ultimately, our cognitive life is all about: truth. Whenever we analyze a scene, whenever we analyze a statement, whenever we recall a memory, whenever we do anything with our brain, we are on a quest for truth.
Our cognitive life is a continuous struggle for truth: is that stain in the distance a tree? Is she home tonight? Will my flight take off on time? Why did the Roman empire fall?
Our mind, ultimately, is an organ to identify truth. The meaing of our life is truth.
The most intuitive theory of truth is perhaps the "correspondence theory of truth", that relates truth to reality: a statement is true if and only if the world it describes is real. Truth corresponds to the facts. The statement "snow is white" is true in virtue of the fact that snow is, indeed, white. The statement "my name is Piero" is true in virtue of the fact that my name is, indeed, Piero. And so forth.
There are several problems with this theory of truth. The truth predicate (the expression "is true") acts as an intermediary between words (language, mind) and the world. One problem is that this definition of truth relates two things that are very different in nature and it is not clear how we can find a correspondence between things that belong to different realms. Precisely, statements (such as "snow is white" and "my name is Piero") are mental objects. They are in my head. The reality we compare them with is made of objects, such as snow. A statement is made of a number of words (each of which may present its own problems at close scrutiny). The reality it refers to is made of objects and properties of objects. Is there truly a correspondece between the words "snow is white" and the fact that snow is white? How can we compared two things that are different in nature, such as a mental object and a physical fact?
This point is important because we are supposed to define truth outside us: truth must not depend on us, it must depend on the world. Something is true not because I think so, but because there is some objective truth out there in the world. If this is the case, the problem is: how can a mental object like a statement relate to an object that is outside the mind.
Second, most statements just do not accurately reflect reality: is snow white? Not really. The closer you look at snow the less white it is. Is today a "hot" day? Yes, if you don't start arguing about which temperature qualifies for hot.
The first objection can be answered by observing that, if you believe in modern science, we rarely talk about things that exist and mostly talk about things that our brain presents us with. I don't know if there exists snow. My brain shows me something that we named snow, but Quantum Physics tells me that there is only a clod of particles. I see white, but Quantum Physics tells me that there is a stream of photons. And so forth. When we say that snow is white, we are not referring to something that exists in the world (it may or it may not exist). We are referring to something that is happening in our brain: our brain received some inputs from the senses and generated the perception of snow and of white. Therefore, both statements and "reality" are mental objects, and it is perfectly legitimate to relate a mental object such as the statement "snow is white" to a mental object such as the perception or the memory that snow is white.
We can rephrase the correspondence problem in neural terms. A statement (for example, about the snow being white) is a neural pattern in the brain. The fact that snow is white is also a neural pattern in the brain (either a pattern of recalling a memory of snow or a pattern of perceiving the snow). It is perfectly legitimate to compare two patterns of brain activity.
The Polish mathematician Alfred Tarski found his own solution to the problems of the correspondence theory.
Alfred Tarski's theory of truth has two components. First, he defines a true staments as a statement that corresponds to reality. This is only a definition of "true statement" and not of "truth" in general. Of course, if one lists all true statements, one gets a definition of truth: truth is "snow is white" and "my name is Piero" and "the Earth is not the center of the universe" and "France won the 1998 world cup" and "..." But this is neither elegant nor practical (most languages have an infinite number of true statements).
The second component to Tarski's theory is the idea that truth can only be defined relative to another language. Most languages include the word "true", but that leads to paradoxes such as "I am lying" which is both true and false at the same time. The problem is simply that "true" is a word of the language and we are applying it to a statement of the language. Tarski realized that one cannot define truth in a language through the language itself and avoid contradictions. So he introduced a "meta-language" to define truth in the "object language". Truth in the object language can then be defined recursively from the truth of elementary statements (the "sentential functions"). "For all sentences s in language L, s is true if and only if T(s) is true", where T(s) is a formula containing s and L's primitives.
Tarski based his "model-theoretic" semantics (models of the world yield interpretations of sentences in that world) on this "correspondence theory of truth" (a statement is true if it corresponds to reality), so that the meaning of a proposition is, basically, the set of situations in which it is true.
Alas, Tarski's theory of truth does not work well with ordinary languages, although it works wonders with the formal languages of Logic.
The problem with Tarski's theory is that it is not clear what he defined. He did not defined truth, but "truth in a language". By this, it is not clear if he indirectly acknowledged that the nature of truth is impossible or even pointless.
A secondary problem is that his theory does not distinguish the linguistic theory from the metaphysical theory: explaining the word "true" is a linguistic matter, whereas explaining the nature of truth is a metaphysical matter.
Tarski's theory is really about the linguistic feature.
Possible World Semantics
In the 1960s the USA philosopher Saul Kripke expanded Tarski’s model-theoretic interpretation to Modal Logic. Modal Logic is a logic that adds two more truth values, "possible" and "necessary" (also know as "modal" values) to the two traditional ones, "true" and "false".
Kripke defined modality through the notion of possible worlds: a property is necessary if it is true in all worlds, a property is possible if it is true in at least one world. Thanks to these two operators, it is possible to discriminate between sentences that are false but have different intension. In classical Logic, sentences such as "Piero Scaruffi is the author of the Divine Comedy" and "Piero Scaruffi is a billionaire" have the same extension, because they are both false. In Modal Logic they have different extensions, because the former is impossible (because I was not alive at the time), whereas the latter is also false but could be true. Also, Modal Logic avoids paradoxes that classical Logic cannot deal with. For example, the sentence "all mermaids are male" is intuitively false, but classical Logic would consider it true (because the sentence "all mermaids are male" translates into a logical formula of the negation of something that is not true, i.e. that is always true). In Modal Logic this sentence is false in the world where mermaids do exist.
The advantage of Kripke's semantics is that it can interpret sentences that are not extensional (that do not satisfy Leibniz's law), such as those that employ opaque contexts (to know, to believe, to think) and those that employ modal operators. Put bluntly, Kripke's semantics can interpret all sentences that can be reduced to "it is possible that" and "it is necessary that". The trick is that in his semantics a statement that is false in this universe can be true in another universe. The truth values of a sentence are always relative to a particular world. A proposition does not have a truth value, but a set of truth values, one for each possible world.
Tarski's theory is purely extensional (for each model the truth of a predicate is determined by the list of objects for which it is true), whereas Kripke's modal logic is intensional. An extensional definition would actually be impossible, since the set of objects is infinite.
Kripke’s semantics can explain how we can refer to a thing by its name, even when we do not know the properties or that thing.
Proper names and definite descriptions are "designators". A non-rigid designator is a term that changes its referent across possible worlds. But proper names are "rigid" designators, i.e. in every possible world they designate the same object ("Piero Scaruffi" is always the same person). So are natural kings: gold is always gold, and water is always water. Kripke (unlike Frege) carefully distinguished the meaning of a designator and the way its reference is determined (which are both "sense" in Frege). If it turned out that water is not H2O, I would still recognize water as water. The term "water" still designates water in a world in which water is not made of H2O.
Kripke’s explanation is his "causal theory of naming": names are linked to their referents through a causal chain. A term applies directly to an object via a connection that was set in place by the initial naming of the object. Initially, the reference of a name is fixed by some operation (e.g., by description), and then the name is passed from speaker to speaker basically by tradition. A name is not identified by a set of unique properties satisfied by the referent: the speaker may have erroneous beliefs about those properties or they may not be unique.
Kripke rejects the view that either proper or common nouns are associated with properties that serve to select their referents. Names are just "rigid designators". Both proper names and names of natural kinds have a referent, but not a Fregean sense. The property cannot determine the reference as the object might not have that property in all worlds. For example, gold may not be precious in all worlds.
Analogously, Jerry Fodor argued in favor of two types of meaning: one is the "narrow content" of a mental representation, which is a semantic representation and is purely mental and does not depend on anything else; and the other is the "broad content", a function that yields the referent in every possible world, and depends on the external world. Narrow content is a conceptual role. Meaning needs both narrow and broad contents.
In the 1980s the USA mathematicians John Barwise and John Perry have proposed "situation semantics", a relation theory of meaning: the meaning of a sentence provides a constraint between the utterance and the described situation. Sentences stand for situations, rather than for truth values. Properties and relations are primitive entities. Situations are more flexible than Kripke's possible worlds because they don't need to be coherent and don't need to be maximal. Just like mental states.
Truth-conditional Semantics: meaning is truth
The USA philosopher Donald Davidson was the main proponent of "truth-conditional semantics", which reduces a theory of meaning to a theory of truth. Tarski simply replaced the universal and intuitive notion of "truth" with an infinite series of rules which define truth in a language relative to truth in another language. Davidson would rather assume that the concept of "truth" need not be defined, that it is known to everybody. Then he can use the correspondence theory of truth to define meaning: the meaning of a sentence is defined as what it would be if the sentence were true. The task for a theory of meaning then becomes to generate all meta-sentences (or "T-sentences") for all sentences in the language through a recursive procedure.
This account of meaning relies exclusively on truth conditions. A sentence is meaningful in virtue of being true under certain conditions and not others. To know the meaning of a sentence is to know the conditions under which the sentence would be true.
A theory of a language must be able to assign a meaning to every possible sentence of the language. Just like Chomsky had to include a recursive procedure in order to explain the speaker's unlimited ability to "recognize" sentences of the language, so Davidson has to include a recursive procedure in order to explain the speaker's unlimited ability to "understand" sentences of the languages.
Natural languages exhibit an additional difficulty over formal languages: they contain "deictic" elements (demonstratives, personal pronouns, tenses) which cause the truth value to fluctuate in time and depend on the speaker. Davidson therefore proposes to employ a pair of arguments for his truth predicate, one specifying the speaker and one specifying the point in time.
In other words, Davidson assigns meanings to sentences of a natural language by associating the sentences with truth-theoretically interpreted formulas of a logical system (their "logical form").
The USA philosopher William Lycan basically refined Davidson's meta-theory. Lycan’s theory of linguistic meaning rests on truth conditions too. All other aspects of semantics (verification conditions, use in language games, illocutionary force, etc.) are derived from that notion. A sentence is meaningful in virtue of being true under certain conditions and not others. However, instead of assigning only a pair of arguments to the truth predicate, Lycan defines truth as a pentadic relationship with the logical form, the context (truth is relative to a context of time and speaker, as specified by some assignment functions), the degree (languages are inherently vague, and sentences normally contain fuzzy terms and hedges) and the idiolect (the truth of a sentence is relative to the language of which it is a grammatical string).
Holism: meaning is relative
The USA philosopher Willard Quine was the messiah of holism.
Quine's theory of "underdetermination" originated in the sciences. Quine was profoundly influenced by an argument put forth by the French physicist Pierre Duhem: that hypotheses cannot be tested in isolation from the whole theoretical network in which they appear. Quine argued that an hypothesis is verified true or false only relative to background assumptions.
For every empirical datum there can be an infinite number of theories that explain it. Science simply picks the combination of hypotheses that seems more plausible. When a hypothesis fails, the scientist can always modify the other hypotheses to make it hold. There is no certain way to determine what has to be changed in a theory: any hypothesis can be retained as true or discarded as false by performing appropriate adjustments in the overall network of assumptions. No sentence has special epistemic properties that safeguard it from revision.
The so called Quine-Duhem thesis reads: no part of a scientific theory can be proved or disproved; only the whole can.
Ultimately, science is but self-conscious common sense.
Language is a special case. The empirical datum in this case is a discourse and the theory is its meaning. There are infinite interpretations of a discourse depending on the context. A single word has no meaning: its referent is "inscrutable". The meaning of language is not even in the mind of the speaker. It is a natural phenomenon related to the world of that speaker.
Quine thinks that the meaning of a statement is the method that can verify it empirically. But verification of a statement within a theory depends on the set of all other statements of the theory. Each statement in a theory partially determines the meaning of every other statement in the same theory.
In particular, the truth of a statement cannot be assessed as a function of the meaning of its words. An individual statement can be proved true or false only relative to the theory they belong to. Words do not have an absolute meaning. They have a meaning only relative to the other words they are connected to in the sentences that we assume to be true. The meaning of a sentence depends on the interpretation of the entire language. Its meaning can even change in time.
In general, the structure of concepts is determined by the positions that their constituents occupy in the "web of belief" of the individual.
In particular, it is impossible to define what a "correct" translation of a statement is from one language to another, because that depends on the interpretations of both entire languages. Translation from one language to another is indeterminate.
Meaning has no meaning. The only concept that makes sense for interpreting sentences is truth. A sentence can be true or false, but what it refers to is not meaningful.
Technically, Quine’s ideas can be expressed in terms of variables. Values of variables cannot be fixed until the interpretation of the whole formal system is fixed (because of a famous theorem in Mathematics, the Loewenheim-Skolem theorem). Thus his famous motto: "To be is to be the value of a variable".
The USA philosopher Paul Churchland expanded Quine's holism by interpreting Quine's network of meanings as a space of semantic states, whose dimensions are all the observable properties. Each expression in the language is equivalent to defining the position of a concept within this space according to the properties that the concept exhibits in that expression. The semantic value of a word derives from its place in the network of the language as a whole.
The correspondence theory of truth assumes that the definition of truth is in the world.
However, one can object that everything is ultimately in the mind and therefore the definition of truth is inside us. It is pointless to look for a definition in the world. Idealists (as opposed to materialists) believe this. This leads to a different theory of truth: truth can no longer be defined as the correspondence to the facts of the worlds, but has to be defined as the correspondence with the facts of the mind. The "coherence theory of truth" defines truth as coherence with the system of beliefs in one's mind: the statement "snow is white" is true if the fact asserted by this statement this is coherent with all the other facts that are believed to be true.
Truth is defined by the set of coherent statements that make up a whole system of beliefs.
Any cosmological theory, for example, is of this kind: the truth of a statement about black holes cannot verified (because we cannot travel into a black hole and not even close to one) and therefore it only depends on whether it is coherent with the other "truths" of Physics.
Idealists believe that this is the only definition of truth that makes sense in general: we can never be sure of the world, therefore we can only assess whether a statement is coherent or not with our beliefs.
The USA philosopher Charles Peirce pioneered the "pragmatist" approach to meaning that amounts to: the meaning of an idea consists in its practical effects on our daily lives. If two ideas have the same practical effects on us, they have the same meaning. He then defined accordingly: truth is the effect is has on us, and that effect is "consensus". Truth is not agreement with reality, it is agreement among humans. That agreement is reached after a process of scientific investigation. At the end of each such process, humans reach a consensus about what is "true" (e.g., that the Earth is not the center of the universe, that water is made of hydrogen and oxygen, that Everest is the highest mountain on the Earth).
Verificationism: meaning is reality
Coherence put truth back into the mind of the observer. Verificationism put it back out into the world.
The British philosopher Michael Dummett criticized holism because it cannot explain how an individual can learn language. If the meaning of a sentence only exists in relationship to the entire system of sentences in the language, it would never be possible to learn it. For the same reason it should not be possible to understand the meaning of a theory, if its meaning is given by the entire theory and not by single components. Dummett's theory of meaning is instead a variant of intuitionistic logic: a statement can be said to be true only when it can be proved true in a finite time (it can be "effectively decided", similar to the intuitionistic "justified").
The truth of a statement must be provable in a finite amount of time, otherwise the statement is not true. The statement "I will never win the Nobel prize" is provable (just wait until I die), but the statement "I am a genius" or "there will never be another like me" are not provable, and thereforetheir truth value cannot be determined. When we say that a statement is true, we mean that it can be verified. Dummett applies to the world at large the same rules that "intuitionists" applied to logic: to decide the truth of a statement is to prove a theorem. The proof determines truth. If no proof can be constructed, then there is no truth. Verification is not just a means to achieve truth: it is truth. The two concepts are virtually impossible to separate.
Similarly, the Finnish philosopher Jaakko Hintikka proposed a "game-theoretical semantics", whereby the semantic interpretation of a sentence is reduced to a game between two agents. The semantics searches for truth through a process of falsification and verification. The truth of an expression is determined through a set of domain-dependent rules which define a "game" between two agents: one agent is trying to validate the expression, the other one is trying to refute it. The expression is true if the truth agent wins. Unlike Dummett's verificationist semantics, Hintikka's is still a "truth-conditional" semantics.
The British psychologist Philip Johnson-Laird too believes that the meaning of a sentence is the way of verifying it. In his "procedural" semantics, a word's meaning is the set of conceptual elements that can contribute to build a mental procedure necessary to comprehend any sentence including that word. Those elements depend on the relations between the entity referred by that word and any other entity it can be related to. Rather than atoms of meanings, we are faced with "fields" of meaning, each including a number of concepts that are related to each other. The representation of the mental lexicon handles the intensional relations between words and their being organized in semantic fields.
Something is true if and only if its truth can be practically verified.
Externalism: meaning is in the society
The USA philosopher Hilary Putnam attacked model-theoretic semantics from another perspective: in his opinion, it fails as a theory of meaning because meaning is not in the relationship between symbols and the world.
Putnam argued that "meaning is not in the mind". Putnam imagines a world called "Twin Earth" exactly like Earth in every respect except that the stuff which appears and behaves like water, and is actually called "water", on Twin Earth is a chemical compound XYZ. If one Earth and one Twin Earth inhabitants, identical in all respects, think about "water", they are thinking about two different things, while their mental states are absolutely identical. Putnam concludes that the content of a concept depends on the context. Meanings are not in the mind, they also depend on the objects that the mind is connected to.
Meaning exhibits an identity through time but not in its essence (such as the momentum, which is a different thing for Newton and Einstein but expresses the same concept). An individual's concepts are not scientific and depend on the environment. Most people know what gold is, and still they cannot explain what it is and even need a jeweler to assess whether something is really gold or a fake. Nonetheless, if some day we found out that Chemistry has erred in counting the electrons of the atom of gold, this would not change what it is. The meaning of the word "gold" is not its scientific definition, but the social meaning that a community has given it. It is not true that every individual has in its mind all the knowledge needed to understand the referent of a word. There is a subdivision of competence among human beings and the referent of a word is due to their cooperation.
Intentionality (the ability of a system to refer to something outside it) is at the center of the philosophical debate on meaning.
Willard Quine’s "instrumentalist theory" rejected intentionality altogether, considering it merely a linguistic trick. Quine thus denied Psychology (that deals with desires, beliefs and hopes and so forth) the status of science.
Daniel Dennett reached a similar conclusion: the intentional stance is simply one of the possible ones, and it is just that, a stance. It is useful to attribute intentional states to other humans, and maybe even to non-human systems. Intentionality is only a feature of our language, a tool. The mind is not intentional because it does not exist, it is only a term in the vocabulary of folk psychology. The brain is not intentional because its states do not refer to anything: they simply are what they are, just like in any physical system.
Jerry Fodor’s representational theory, instead, posits that the brain literally contains the intentional state that we ascribe to the mind. For Fodor, the vocabulary of folk psychology "is" a scientific language: it describes facts that are really happening in the brain, not just linguistic tools.
The USA philosopher Ruth Millikan argued that intentionality is an objective, natural, biological feature of humans, that evolved over millions of years just like any other organ or limb of the human body. Intentionality is no more than the biology of belief, desire, hope and intention, which must be treated like any other biological object. Propositional attitudes (beliefs, hopes, desires, intentions) are biological devices, designed by evolution to have some effects on us. That effect is its content. Thus the effect has been determined by evolution. This strategy of treating intentionality as a biological feature can be extended to treating meaning as a biological phenomenon ("biosemantics"), because each sentence can be viewed as having a biological function (typically, helping us live in the world). "Sentences are basic intentional items". Intentionality is grounded in the relationship with the environment, a relationship determined by evolution. A mental content is the effect of a biological system designed by evolution to have that effect. Presumably, Millikan believes that desires and beliefs are physiological features of the brain, because they have evolved from generation to generation just like any other bodily organ has. On the other hand, the contents of these beliefs and desires are located outside the brain, and can be understood only by understanding their biological function, i.e. their evolutionary history. A belief is similar to the dance of a bee, a biological feature designed by evolution that refers to an object outside the head of the bee.
The "externalist theory" of the British philosopher Colin McGinn’s is an extension of Millikan’s teleological theory. The mental content of humans is external to their minds for the simple reason that it was set by evolution and it refers to the environment. The cognitive life of humans has been shaped by evolution to cope with an external object, the environment. Beliefs and desires are brain states whose content is a relation to the external world.
The information-processing theory of the USA philosopher Fred Dretske assumes that cognitive life consists in transforming analogue information (that comes from the sensory system) into digital information (that can become the processed as knowledge). For example, a smell per se is only a set of sensory data. Once it is analyzed and turned into the information that it corresponds with the smell of a particular flower, we "know" a fact about the world. This transformation from analogue to digital is what creates a "belief". A belief is therefore a neural structure. This is what the system "believes". The content of that belief is thus defined by its informational origin and not by its behavioral effect. A concept is the link between the information origin and the behavioral effect. The semantic content becomes a cognitive content when it is transformed from a representational unit to a functional unit.
In the functionalist theory of the British philosopher Brian Loar beliefs and desires are real physical states with real causal powers, but they are wholly defined by and within the overall network of beliefs an desires. A belief is defined by its functional role within the network of the person’s beliefs. In a sense, the mind "is" the network of prepositional attitudes.
The USA philosopher John Searle thinks that intentionality can only be relative to a contextual "network" of other intentional states and to a "background" of pre-intentional stances. The background is necessary for the network to function. In other words, in order to perform a mental act, one must have a network of mental acts and they must be grounded in the real world. For example, I can "desire to see a film" only if I believe that the film exists and is showing. Thus the "network". And i can go and see the film only if I know how to drive the car and how to find the address. Thus the "background".
Of course, one can also claim that truth simply does not exist, and that is why it is so difficult to define.
In 1927 the British philosopher Frank Ramsey inaugurated "deflationary" thinking about truth by claiming that the word "true" is simply redundant: "it is true that the snow is white" does not say anything more than "the snow is white". By adding "it is true that" we are not adding anything: we are merely making it sound nicer.
Quine's "disquotationalism" follows from this claim: to ascribe truth to a statement merely means to remove the quotation marks.
For example, the statement "snow is white" is true if and only if it is a fact that snow is white. Now remove the inessential words and what you have is: "snow is white" is true if and only if snow is white. The truth predicate "is true" simply removes the quotation marks.
"Truth is disquotation". Quine concedes that the truth predicate (the expression "is true") has at least one useful function: it allows us to generalize, like when I state "everything I told you is true". By using the truth predicate, I can simplify what would otherwise be an infinite list of statements. But this is the only usefulness of the truth predicate: there is no need for a theory of truth, there is no nature of truth. The truth predicate is merely a linguistic expedient to generalize statements.
The problem remains, of course, that ordinary humans can easily grasp the concept of "true", whether Quine believes it to be a mere "disquotation" or not. There is something that we call "truth" in our minds.
Donald Davidson argues that truth is a primitive concept that cannot be defined via any other concept. In fact, no other concept would exist without the concept of truth.
Ludwig Wittgenstein proposed a common-sense theory of truth: different statements can all be true without being true in the same way. This idea led him to "alethic pluralism", i.e. to accept that truth is a multi-faceted concept.
Likewise, the USA philosopher Michael Lynch takes issue with the idea that there is "one" theory of truth. Lynch argues that there is a plurality of "truths", rather than a single all-encompassing theory of truth. For example, truth in ethics and truth in justice and truth in mathematics obey different laws. The nature of truth is difficult to find because there isn't only one nature of truth. One needs a different theory of truth for each domain, and that is precisely what ordinary humans employ in their daily lives.
Just like functionalism believes in "multiple realizations" of the same mental phenomenon, i.e. that the same mental state can be "realized" by different physical states (what matters being the function, not the "stuff"), Lynch believes that "truth" (a uniform concept across domains) can be realized by different theories in different domains.
For example, pain is a mental state that is causally related to some inputs (e.g., a sore finger), outputs (e.g., facial expression and sounds), and other mental states (e.g., unhappiness). Any state that realizes this causal role is called "pain", even if the pain due to a blister and the pain due to a cold are very different in nature.
Lynch claims that "truth" names a functional role, and that we all understand what that role is, regardless of what realizes it. Lynch compares this with the concept of "head of state": both the president of the United States, the king of Jordan, Fidel Castro and the chancellor of Germany are heads of state, although the way they got the job and the way they administer it vary greatly. The "function" of head of state, though, is understood the same way in the US, France and Cuba.
(A possible objection is that equality is sometimes merely a form of fuzziness: the closer you look, the less similar Castro and the king of Jordan are, and the less clear the term "head of state" is. One can suspect that "functional role" is a synonym for "vague definition". Relax the definition and just about anything in this universe will have the same "functional role" as anything else).
If truth is merely a functional role, if "to be true" is to play the "alethic" role, what is exactly that role?
Lynch thinks that truth is defined by an "alethic network", a set of interdependent definitions that, jointly, define each other: a proposition is whatever is true or false, a fact is what makes a proposition true or false, etc. Lynch claims that each "alethic concept" in the alethic network is defined by the role it plays in the network. One cannot grasp an alethic concept (truth, proposition, fact) without grasping them all. Each alethic concept depends on all of the others. Truth cannot be defined as "stand alone", but only as part of the broader definition of all alethic entities.
Truth is the property of playing the truth role in an alethic network.
There is one and only one concept of truth, but it can be realized in multiple ways.
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