It is now almost fifty years since Kripke made his celebrated distinction between epistemic and metaphysical necessity.He pointed out that not all necessary truths are known a priori: for example, it is not a priorithat this table is made of wood, but it is a necessary truth—this very table could not have been made of plastic. Similarly for water and H2O, heat and molecular motion, a person and his origin, an animal and its species, etc. Since these necessities are not a priorithey are not analytic, i.e. a consequence of the concepts involved. Thus it follows that they do not depend on our concepts: they do not arise from the content of our thoughts or the meaning of our words. To that extent they are not mind-dependent. It would be tempting to conclude that Kripke established the objectivity of necessary truths: he established that there are necessary facts obtaining independently of minds. This table would necessarily be made of wood even in the absence of human beings and their minds (or any other form of intelligence). Kripke certainly talks this way, without making explicit that he is affirming modal objectivity. If necessity doesn’t depend on our concepts, but on “the world”, doesn’t it follow that it obtains independently of minds? And isn’t it intuitively obvious that water is necessarily H2O whether or not anyone refers to or thinks about water?Likewise, isn’t it obvious that water is only contingently found on earth whether or not anyone talks about water? Aren’t these objective modal facts once we distinguish them from analytic and a prioritruths? So doesn’t Kripke’s distinction establish modal objectivity? I certainly have assumed as much for the last fifty years.
But the matter is not so obvious on reflection: for there are other ways to formulate modal subjectivism than by equating necessity with analytic or a prioritruth. So the correctness of Kripke’s distinction does not entailmodal objectivism. For instance, one might claim that modality consists in dispositions to produce impressions of modality—as color consists in dispositions to produce impressions of color.Thus for this table to be necessarily made of wood is for it to be disposed to cause in subjects the impression that it is necessarily made of wood. If that were so, the necessity would not be mind-independent; in the absence of minds there would be no such modal fact (compare colors). In other words, if modal properties were secondary qualities they would not be objective. And to be a secondary quality is not to be a priorior analytic: it is not a priorior analytic that this table is brown, but being brown is mind-dependent (assuming the dispositional analysis of color). Thus modal subjectivism is logically compatible with accepting Kripke’s distinction. For all Kripke has said, modality is entirely in the mind not in the world, de mentenot de re. Similarly, someone who believes that necessity arises from our practices of individuation will also reject strong modal objectivism, since necessity will then depend on the human agent. Suppose it is claimed that we individuate the table by means of its composition not by its location (since it moves around) and that is why we rate its composition as necessary. Such a theorist would be committed to a mind-dependent view of so-called metaphysical necessity. The impression of necessity is a function of our practice of identifying and re-identifying objects; there is no more to it than those practices. Or again, suppose the theorist is an expressivist in a variety of domains (ethics, aesthetics, probability) and wishes to apply this doctrine to modality, holding that “This table is necessarily made of wood” merely expresses an attitude about the table not a fact about it. It is a fact that the table is made of wood but not a fact that it is necessarilymade of wood—that is no more an objective fact than the “fact” that torture is wrong. Both are expressions of human sensibility. Such a view implies that modality is not an objective matter—a matter of facts obtaining independently of human sensibility. But it is not the doctrine that all necessity is a priori. Modal subjectivism can take other forms.
Now it is not that I take any of these views seriously: I am a convinced objectivist about the metaphysics of metaphysical necessity. I am merely indicating a gap in the argument for modal objectivism. The question is how to close this gap, given that Kripke’s distinction isn’t sufficient. And here the matter grows murkier—more profound, if you will. For it is not clear how to argue for the objectivist position: we have here a clash of basic intuitions. The modal subjectivist can’t see how objective reality could contain modal ingredients to be set beside tables, piece of wood, particle and planets–as she can’t see how values can exist objectively alongside facts. The modal objectivist prefers a more expansive view of reality and recoils at the idea of consigning necessity to the subjective world. How can we decide between these views? It is no use appealing to intuitions about what reality would contain in the absence of minds, because those intuitions are likely to conflict according to philosophical predilection. However, there is a type of argument that can at least focus the issue—and which to my mind settles it in favor of objectivism. This is what we can call an inversionargument, familiar from discussions of color. What if Martians see as green what we see as red—would they be wrong? Intuitively the answer is no: they would simply see the same objects differently. Objects have color only relative to a chosen class of perceivers, not in themselves. By contrast, if Martians see as circular what we see as rectangular, one of us would have to be wrong—because shape is objective. Where does modality fall? What if Martians were under the impression that the table is contingently made of wood and necessarily located in a certain place—would that just be a matter of their subjective response, true relative to them? I think not: they would be wrong so to suppose. Clearlylocation is not an essential property of the object, and clearlycomposition is. Likewise, it is not a relative matter whether water is necessarily H2O and contingently in my cup—anyone who thought otherwise would be wrong. The same point can be made about the expressivist and the enthusiast of individuation: inversion does not preserve truth. Modality does not track response; it can falsify response. Modal truth is not response-dependent. So now we have an argument in favor of modal objectivism and can relax into the mode of speech Kripke found so natural, in which we speak of necessity as de re, in the world, an aspect of objective reality. The table in itself is necessarily made of wood no matter what anyone thinks, and water is necessarily H2O irrespective of anyone’s impression. Even if no intelligent beings had ever existed de renecessities would still exist, and contingencies too. Not only is necessity independent of concepts; it is independent of anything mental. Not only are there metaphysical necessities; there are objective metaphysical necessities.
Hume provides the locus classicusof this type of view: causal necessity consists of nothing more than our habit of moving mentally from cause to effect when exposed to constant conjunctions—we project causal necessity onto the world. At least that was the traditional interpretation of Hume, which I reject (along with many Hume scholars): the correct view is that he believed in objective causal necessity but thought we could have no adequate idea of it, though we do have a kind of surrogate idea deriving from our inner inclinations. At any rate, the traditional interpretation gives a model for the type of subjectivism I am interested in describing (but not endorsing).
It is completely unclear to me from Kripke’s text whether he subscribes to modal objectivism as a piece of metaphysics, since he says nothing explicitly on the question; but his general style of talking indicates that he would accept it.