Back to Main MenuI. Introduction
As we saw last time, there are several interesting issues regarding the questions of meaning, reference, and necessity. The two theories of meaning we examined there, the naive referential theory and possible worlds semantics, each gave an account of meaning that was not psychological. In other words, the meaning of terms is not to be identified with psychological entities such as mental representations. Today, we will tackle this problem from a different angle, once more asking the question, "Are meanings 'in the head'?" According to philosopher Hilary Putnam, the answer to this question is clearly no. We will examine his arguments for this view, and what they imply about necessity.
II. Twin Earth
Suppose that there is another planet somewhere in the universe (or a universe in another possible world, since the following story may not be possible given the actual laws of physics!), which is exactly like Earth was in 1750 in nearly every respect. That is, observation could not distinguish the two worlds: the continents look the same, the course of history up to 1750 is qualitatively the same, the people look exactly like their counterparts did on Earth in 1750, and so on. We will call this planet "Twin Earth." There is only one respect in which Twin Earth differs from Earth: the substance we call "water" here, and which our counterparts on Twin Earth call "water" (their language in the counterpart of England and its colonies sounds the same as English did in 1750), does not have the chemical structure H2O, but a different chemical structure, call it XYZ. This substance is tasteless, and the Twin Earthlings drink it, bathe in it, wash things in it, and so on, the same as Earthlings. Question: Is this liquid water? Be careful to distinguish this question from the superficially similar question of whether Twin Earthlings call it "water." They do; that's part of the story. The question is whether it is water, or a substance that happens to look and behave just like water.
According to Putnam, Twin Earth has rivers of XYZ, rains XYZ, and its inhabitants use XYZ the same as we use water, and yet Twin Earth has no water -- it has XYZ instead. This, he believes, is obvious, and not intrinsically interesting. The interesting thing is what it tells us about the nature of meaning. What did the term "water" mean in English in 1750, and what does that term mean in the similar-sounding language on Twin Earth? The answer is that "water" in English referred to the substance that we now know (though they did not) has the chemical structure H2O. That was the meaning of the term then; it is the same thing "water" means now. When chemists in the early 19th century discovered that water was H2O, they did not give the word "water" a new meaning; rather, they discovered what water (in the meaning it had before the discovery) really was. Since the psychologies of the Twin Earthlings are, narrowly speaking, the same as the psychologies of Earthlings in 1750 (a person on Earth and his or her counterpart on Twin Earth have the same mental representations, though these representations might have different contents, as we shall soon see), it follows that the set of psychological entities (mental representations) that are "in one's head" does not determine the meaning of one's linguistic uttrerances, nor do they determine the content of one's thoughts. An Earthling may be thinking about a tall, cold glass of water on a hot day, but a Twin Earthling with a formally similar mental life is thinking no such thing: he is thinking about a tall, cold glass of XYZ, which he calls "water" (a term that in his language means something different from what we mean by the term). Thus, Putnam argues, meanings are not "in the head"; a person's mental life does not by itself determine the meaning of that person's language.
Putnam wants to argue that this true not only of water, but of other natural kind terms as well -- the terms "gold," "silver," "dog," "cat", "jade", "person," and so on all have their meanings determined not only by the way we intend to use the term, but also by the nature of the things to which we apply the term. I may think of "gold" as a shiny yellow substance worth a lot of money, but that is not what "gold" means when I use the term; rather, it refers to a particular type of chemical element. The methods I use to determine whether something is gold also do not determine the meaning of "gold" for me; there are "gold experts" in my community which hold the definitive tests for whether something is gold. That is, there is what Putnam calls a linguistic division of labor: some people in a linguistic community have more expertise in determining whether something falls into a certain category, and that fixes the reference of the term for my linguistic community. (This does not imply, of course, that the experts know everything there is to know about the ultimate nature of that substance. Their methods for identifying gold determine what the term "gold" applies to, but the meaning of the term "gold" is not to be identified with the collection of methods they use to identify gold.)
III. The Nature of Intensions, and Metaphysical versus Epistemic Necessity
If Putnam is right, then "water is H20" in some sense expresses a necessary truth (or a necessary falsehood, depending on what the term "water" means in the speaker's linguistic community). Nothing would count as water if it is not H20; hence, there is no possible world in which there is water that is not H20. This is true because water is H2O, not because people in a given (English-speaking) community would all assent to the sentence "water is H2O." (As we saw, no one would have assented to this claim in 1750; nevertheless, when they were talking about water, they were talking about H2O.) This is all very puzzling, however, since "water is H20" seems to have a very different status from "water is water." We can easily imagine a person, call him John, believing that water is water without believing that water is H20 (this would include everyone who had beliefs about water before the chemical makeup of that substance was discovered). There had to be a significant amount of scientific investigation before the truth of "water is H20" was decided; this is not the case with statements such as "water is water" or "bachelors are unmarried males" which are either trivially true, or true by definition. These statements therefore appear to have very different kinds of epistemic staus: a person can know that "water is water" is true without thereby knowing that "water is H2O" is true. Thus, it might be argued, the terms "water" and "H2O" do not seem to be synonymous: if they were, then learning the meaning of the terms "water" and "H2O" should be sufficient by itself for determining the truth of "water is H2O," just as once a person learns the meanings of "medical doctor" and "physician," he does not have to conduct any studies or gather observations to determine whether medical doctors are physicians. That they are follows from the meaning of the terms. In what sense, then, do "water" and "H2O" have the same meaning?
According to Putnam, what the Twin Earth thought experiment shows is that the following two statements cannot both be true.
Putnam rejects the first statement, and retains the second. It is obvious however, that psychology and the speakers' intentions play some role in how a term acquires its meaning. "Water" means what it does because people in a certain linguistic community use the term "water" to refer to a substance in their environment that is drinkable, tasteless, colorless, nontoxic, thirst-quenching, etc. All of these properties are part of the community's "stereotype" of water: in other words, they are the properties that members of the community associate with and use to identify water. (If a term is technical, such as "gold," its stereotype may be known in its entirety only to certain "experts" in a given community, according to the linguistic division of labor discussed above. Everyone, however, counts as a "water expert.") According to Putnam, the meaning of a term is not to be identified with a stereotype; nevertheless, the stereotype should be considered part of the meaning of the term. Similarly, the concepts of sense and intension (discussed last time) cannot be identified with a stereotype. What the stereotype does is to fix the reference of a given term, rather than to give the meaning of a term. When a person coins a new word such as "water", he or she uses the term to refer to a certain thing (such as a substance in a lake), and intends the term to apply to everything that is of the same kind as the substance in the lake. Given that the substance in the lake is H2O, this means that "water" thereby refers to H2O. If we in a particular linguistic community use a single term to refer to more than one type of thing (such as "jade," which refers to two superficially similar substances, jadeite and nephrite), then its meaning is any thing of the same kind or kinds as the things we have been referring to using that term (i.e., jadeite or nephrite). To sum up, Putnam would argue the following. The meaning of "water" consists of its extension, which is determined by whatever we single out in the world using the stereotypical properties we use to identify that kind of thing, and the stereotypical properties (as well as other things, such as various syntactic and semantic "markers"). "Water is H2O," as uttered by an English speaker on Earth, is necessary (or, as one might say, metaphysically necessary) in the sense that nothing could be water that is not H2O. The term "water" is a rigid designator: it refers to the same (kind of) thing in all possible worlds, just like names such as "Bill Clinton," or indexicals such as the "I" in the statement "If I were President, I would do things differently." (The "I" here refers to the speaker, not to Bill Clinton; if Bob Dole utters it, the statement means that in a possible world in which Bob Dole is President, Bob Dole would do things differently than Bill Clinton.) Thus, natural kind terms such as "water" resemble indexicals like "I," "here," and "now" (here the "index" is the thing or type of thing to which the term is used to refer in the speaker's actual linguistic community). "Water is H2O" is epistemically contingent (not necessary), however, since the property H2O is not part of the stereotype of water; scientific investigation was needed to determine whether or not water is H2O.