...The accessibility relation is important to modal logicians because the formal features ascribed to it by a particular semantic interpretation explain the truth of the characteristic axioms of the formal system being interpreted.  But my purpose in this chapter is to show that variations in accessibility are, if anything, even more important linguistically, and philosophically.  In particular, I shall give several examples of knotty philosophical issues that become more tractable once they are approached as questions about accessibility.

     No ordinary English sentence expresses an unrestricted alethic modality.  Rarely do we hear mention of logical necessity, logical possibility or entailment  outside a philosophy department.  Indeed, many undergraduates have trouble grasping the concept of barely logical possibility, even with professional help.
     Rather, all everyday modalities are restricted, relative to contextually determined sets of background assumptions.<1>  That is both unsurprising and a very good thing.  Interestingly, though, few of even those street-level restriction classes themselves correspond to recognizable philosophical categories.<2>  As a case very much in point, the concept of natural or physical necessity is hardly better known to everyday English than are the purely alethic modalities.  I shall give some examples of real restriction classes.

1. MODALITIES IN NATURAL LANGUAGE

    The syntactic behavior of what have traditionally been called "modal auxiliaries" in English  reflects the drastic semantic/pragmatic context-dependence of modal notions.<3>  Sometimes it is revealed in an unexpectedly specific though still tacit restriction: "That woman speaks eighteen languages and can’t say ‘No’ in any of them" (attributed to Dorothy Parker).  Sometimes it is revealed in an oxymoron: "I have to, but I can’t."<4>  For some further examples, consider the following passage from a rather good trash novel of the 1960s:<5>
     Boo and Ira have been conducting a parodically torrid adulterous affair.  They are now talking by ‘phone.

     "I have to see you, Ira.  As soon as possible.  I’m going out to the beach house this evening at six o’clock to talk to a man who’s building a new jetty.  I’ll surely finish with him in a half-hour or so.  Could you meet me out there at seven o’clock?"
     "How can I, Boo?  At eight o’clock I’m doing the telecast from Acanthus."
     "That’s right, I forgot," she said.  "All right, then, how about this: I’ll wait at the beach house and you can meet me there when you finish the telecast.  Okay?"
     "But you’ll miss the program.  You don’t have a tv set at the beach."
     "I know, Ira, and I’m terribly sorry.  But this is more important.  Please, please, my darling, I have to see you tonight!"
     Elation came galloping back to Ira.  "Yes, yes, tonight!" he cried.  "Tonight!  Yes!"
     "At the beach house."
     "Yes, my darling.  Yes, my good, sweet-- "  Elation made another quick retreat.  "What do you mean, you ‘have to’ see me?" he said warily.  "Do you mean it’s like an emotional need?  For example, when two lovers are kept apart for a length of time, there is a certain psychic compulsion to be reunited.  Is that what you had in mind?"
     "Ira, I can’t talk any more.  There are people in the house."
     "Wait, wait, wait!" he insisted.  "I just want to clarify this one point.  It boils down to those words ‘have to.’ Could you possibly be a little less ambiguous?"

     "I have to_[1] see you, Ira.  As soon as possible_[2].  I’m going out to the beach house this evening at six o’clock to talk to a man who’s building a new jetty.  I’ll surely finish with him in a half-hour or so.  Could_[3] you meet me out there at seven o’clock?"
     "How can_[4] I, Boo?  At eight o’clock I’m doing the telecast from Acanthus."
     "That’s right, I forgot," she said.  "All right, then, how about this: I’ll wait at the beach house and you can_[5] meet me there when you finish the telecast.  Okay?"
     "But you’ll miss the program.  You don’t have a tv set at the beach."
     "I know, Ira, and I’m terribly sorry.  But this is more important.  Please, please, my darling, I have to_{[= 1]} see you tonight!"
     Elation came galloping back to Ira.  "Yes, yes, tonight!" he cried.  "Tonight!  Yes!"
     "At the beach house."
     "Yes, my darling.  Yes, my good, sweet-- "  Elation made another quick retreat.  "What do you mean, you ‘have to’ see me?" he said warily.  "Do you mean it’s like an emotional need_[6]?  For example, when two lovers are kept apart for a length of time, there is a certain psychic compulsion_[7] to be reunited.  Is that what you had in mind?"
     "Ira, I can’t_[8] talk any more.  There are people in the house."
     "Wait, wait, wait!" he insisted.  "I just want to clarify this one point.  It boils down to those words ‘have to.’ Could you possibly_[9] be a little less ambiguous?"

     (1) "I have to see you...."  My seeing you is required by some contextually specified external circumstance (not just the pregnancy, but Boo’s reason(s) for informing Ira of the pregnancy); the modality itself is (further) relativized to whatever psychological and/or social norms apply.  A very long story, though in part because drastically underdescribed.
     (2) "...as soon as possible."  As soon as is consistent with...?  The modality here centers on Ira and both the norms and the circumstances centered on him; but I think it is also constrained by Boo’s situation and norms applying to that.
     (3) "Could you meet me...?"  Possibly the same as (2), but I doubt that.  "Possible" in (2) grammatically applies to the infinitival complement of "I have to see you," or some suitably nominalized version of it such as "my seeing you"; but "Could" in (3) is the head of a VP predicated directly of the subject "you" (= Ira), suggesting a closer connection with Ira’s own circumstances and less to do with Boo’s situation.
     (4) "How can I, Boo?"  Someone might think that (4) is the same modality as (3), but the identity is unlikely.  "Could" in (3) and "can" in (4) are not related as past tense and present.  Rather, "could" is subjunctive where "can" is indicative; and (as is conceded by all parties, whatever may be the deeper analysis) the subjunctive introduces a wider range or larger space of possibilities than does the more actuality-oriented indicative.<7>  Perhaps in a more remote sense Ira could meet Boo, but as things are he cannot.  Yet this "can" has nothing to do with Ira’s abilities or even with his legal situation; it hovers somewhere between his institutional responsibilities (to the television network that employs him) and simple prudence.  N.b., the negative answer to Ira’s rhetorical question is something that Boo is mutually presumed to know but admittedly has forgotten, and it trumps her more remote "could"; they are neither disagreeing nor talking past each other.
     (5) "...[Y]ou can meet me there...."  In the absence of further context, this is a tough one, but I hear it as well paraphrased by something between the same "can" as (4) and "[Then(?)] it’s OK [with me] if you just meet me...."  It is not simply the same "can" as (4)’s, which occurs within the scope of "How about...?"
     (6) "...an emotional need [to see me]."  The concept of "need" is tricky, but I think White (1975) is correct in maintaining that any felicitous token of "need" tacitly refers to a contextually indicated goal or end-state, and the idea is that the needed state of affairs is necessary for the realization of that end-state.  (There is no particular universal or even default end-state.<8>)  "Emotional" here begins to classify the relevant end-state envisaged by Ira.  But the underlying sort of "necessity" is vexed and (at least) needs<9> much further unpacking.
     (7) "...a certain psychic compulsion...."  Here the modality occurs as a noun, but the noun is a derived nominal (from "X compels Y") and needs<10> an underlying subject, an agent or other being that does the compelling--here, presumably, Boo’s psyche conceived as necessitating her reunion with Ira by acting on her.<11>
     (8) "...I can’t talk any more."  This, suddenly, has nothing to do with Ira’s situation and proceeds entirely from Boo’s immediate circumstances.<12>  Her talking any more would be (as things are) incompatible with privacy, or with discretion on her part, or with prudence.  (Those are the candidates nominated by the novel’s surrounding plot.  But others are at least consistent with the portrayed facts:  She may be flat out of emotional energy; her sanity, or his, might be at stake; an armed guard might be about to grab the phone; etc.)
     (9) "Could you possibly be...?"  Another toughie, in part because we are not sure whether Ira is being ironic.  If we assume he is not, we still need to know whether "Could...possibly" is (a) a merely emphatic redundancy, (b) a compounding of two distinct modalities, or (c) something in between, such as a widening of the range of the first modal operator by the second.  In any case Boo’s presumed constraints are quite indefinite.  They are unlikely to be the same that control the modality in (9); a direct reply to (8) would refer more directly to the presumed constraints, rather than to the semantic interpretation of her utterance (as, e.g., "Could you possibly hang tough and also put a few more quarters in the ‘phone?").

     Again, though the foregoing comments are intended to be roughly true, they are at best impressionistic; not one is put forward as having much analytical value.<13>  My purpose is only to indicate that everyday English is shot through with restricted alethic modalities whose restrictions are almost capriciously diverse, rarely aligned with any easily specifiable modal concept known to logicians, and irreparably vague--yet calculated on the spot by ordinary human speakers/hearers with hardly a conscious thought.  The rate of modal montage exhibited in the Boo-Ira exchange is remarkable, and the linguistic competence involved in our rapid interpretive shifts is simply amazing.
     Notice particularly that the philosophers’ idea of nomic or physical necessity plays no role here.  Genuine laws of nature are thin on the ground in any case,<14> and surely none of them applies to matters such as Boo’s reasons for informing Ira of the pregnancy, Ira’s institutional responsibilities, Boo’s eventual reunion with Ira, her privacy and discretion, etc. (even if those items are supervenient causes or effects, connected under lower-level descriptions by the laws of some natural science).  Rather, the modalities in question seem representable only by accessibility relations that are themselves unphilosophical and vague.  I suspect that that vagueness is part of the human condition.<15>
     Further and often even more idiosyncratic examples are provided by the "-ble" suffix attaching to verbs.  Consider:  (1) A person commits an unspeakable act (howler, solecism, faux pas, outrage,...).  That means the tale cannot be told without--I would say--scandal, or the mention of things whose very mention offends propriety; it certainly does not mean that no one has the ability to tell it, or even that telling it is illegal.<16>  (2) A person says something unprintable or unrepeatable; that normally means the person used taboo words, though "unprintable" might alternatively mean something forbidden by journalistic ethics.  (3) Physical things and stuffs can be inedible in various ways--but usually not in the sense that such a thing simply cannot be eaten, as holds for the Eiffel Tower or the Earth itself.  Cyanide is inedible in that one cannot eat it and survive.  A used milk carton is inedible in that eating it has no nutritional value and may cause one some considerable intestinal distress.  Mice are classified as inedible creatures in that, even though they are nutritious, eating one is (I am not sure which:) potentially unhealthful, or disgusting, or socially proscribed, or perhaps otherwise a very bad idea.  A local greasy spoon’s food is inedible in that one cannot normally even make oneself eat it, though one might manage to gag it down at gunpoint; but a pretentious restaurant’s food might be inedible only in that its low quality is grossly incompatible with the restaurant’s pretensions and prices, and/or with the gourmet’s minimal standards.  (4) Pharmaceutical companies advertise "chewable" aspirin.  In context, this could hardly mean "can be chewed," or even "can be chewed without such-and-such physical damage"; it means something like, "can be chewed without seriously offending the taste buds."
     This list could go on and on and on.  I trust that, once the reader has got the idea, he/she will see the phenomenon everywhere.  Indeed, a careful reading of this very chapter will yield scads of examples, and not because I tried to put them there.
     Notice further that some alethic modalities are not reflexive.  (It is well known that deontic and doxastic modalities are not reflexive, since what ought to obtain and what is believed to obtain may not in fact obtain, but one would naturally think that any alethic modality would support  Nec(p) |-  p and its dual,  p |-  Pos(p).)  The previous example, "I have to, but I can’t" already demonstrates the point, but here is a striking example from a biography of Henry Kissinger:<17>

Later, Kissinger would wonder about the interview [that he had given to Oriana Fallaci on November 4, 1972] and sigh, "I couldn’t have said those things, it’s impossible."  But he never denied it.

1 When the context fails to supply any very specific cue, a modal assertion is often utterly pointless:

 "And the insurance?" Callaway asked.  "When may the beneficiaries expect to have the claim approved?"
 Dora smiled sweetly.  "As soon as possible," she said, and shook his hand.

2  Lewis (1973, pp. 6-8) expounds the relativity of modality splendidly, but very much in terms of recognizable philosophical categories.

3  Even in modern times, grammarians have used a variety of criteria for picking out "modal" verbs as a subclass of auxiliaries.  See Joos (1964), Palmer (1965), Ehrman (1966), Lyons (1968), Greenbaum (1969), McCawley (1988, Ch. 8).   Everyone seems to agree on at least the following as modal auxiliaries: "can," "could," "may," "might," "must," "have to," "shall," "should," "will," "would," and "ought."  "Need to" is only slightly controversial.

4  In his Memoirs  (1991, p.13) Kingsley Amis recalls telling his young sons about sex, and ends the story with the sentence, "In no sphere is it truer that it is necessary to say what it is unnecessary to say."

5  Max Schulman’s Anyone Got a Match? (New York: Bantam Books edition, 1965), pp. 192-3.  My eye happened to fall on this passage; any reader can find similar examples with little effort.

6  I hope there is no longer anyone who thinks that the differences here reflect lexical ambiguities in modal words.  (Aune [1967] pretty clearly sinned in this regard; Gibbs [1970] is a possible but unconfirmed villain.)  Such ambiguities would be monstrous.  The point has already been well made by Margolis (1971), by Wertheimer (1972), by White (1975) and by Kratzer (1977).  Instead, the accessibility relation is the perfect device for exhibiting the "ambiguities" as pragmatic.  (Yet White further argues convincingly for a very general and widespread pragmatic but syntactically marked distinction between "existential" (roughly metaphysical) possibility  and "problematic" (roughly, but only roughly, epistemic) possibility.)
     Incidentally, both Wertheimer and White are badly undercited, presumably because underread, by modal philosophers and by linguists.  Moreover, Wertheimer is undercited by White, and Kratzer cites neither.

7  It is of course possible that Boo’s whole utterance has derived illocutionary force, and is simply an indirect request; such requests can be performed using "Could you...?" as a semiconventional locution (Morgan [1978]; Lycan [1984, pp. 178-81].  But here I think Boo’s utterance can just as well be heard literally.

8  If there were, I suppose it would be staying alive.  But even terminal patients who have not the slightest prospect of staying alive much longer can need things unconnected with staying alive.  There are similar counterexamples regarding the nearly universal goals of being happy and having all one’s desires fulfilled.   For interesting further discussion, see Stampe (1988).
    Also, a need may be ascribed to one person while the relevant end-state resides in another person:  "You need to take out the garbage."

9  Sorry.

10  Sorry again.  Notice that "need" does not need (s.a.) an animate subject, as is well argued by White (1975, pp. 104-5).

11  Though, unlike "compel," "compulsion" is sometimes used with less than success-grammar; one may have a compulsion to do something and manage to refrain from doing it.

12  Notice that (8)’s paraphrase in terms of "possible" is far better complementized by "for...to" than by "that":  "It is not possible for me to talk any more" is lots better in this context than "It is not possible that I talk any more."  Some relative modalities may be syntactically and semantically, not just pragmatically, pegged to individual subjects.  The application of this idea in modal logic was explored by Hilpinen (1969).

13  Wertheimer (1972, Ch. Three) and White (1975) make excellent starts on a real analysis.

14  If there are any.  I take it to be controversial that there exists any alleged law of nature that is (a) true, (b) strict and exceptionless, and (c) indeed physically necessary, in the sense of some event’s being even hypothetically ruled out by (because logically incompatible with) a set of basic scientific principles that are themselves strictly true.  Perhaps "Nothing, relative to any reference frame, travels faster than the speed of light" is such a law.

15  Noting that a speaker need not be able to specify any one "System" (or set of background conditions or accessibility relation), Wertheimer (1972, p. 92-5) tries to resolve the vagueness by prefixing an existential quantifier:  "NP Nec_(whatever) VP" is true iff "there exists an adequate relevant System," i.e. (p. 95) a System of the relevant kind.  But the vagueness persists, in "relevant."  An hearer may be capable of working out that a particular "must" is moral in kind; but vagueness remains within the category of morality, and the same hearer would in any case have got as far as that category without having to compute an existential quantification.

16  Interestingly, "unspeakable" cannot be replaced in this context by "unsayable."  Indeed it is hard to say, out of context, what the result of that replacement might mean.
     It is also interesting to observe that some modal adjectives of this type take intensifiers and/or comparatives: "That glass is very breakable"; "Compound A is more soluble than compound B."  A true linguistic Nazi (I myself border on being such a person) might insist that "very breakable" be replaced by "very readily breakable" and "more soluble" by "more readily soluble"; but that seems pedantic, and there would remain the question of why a purely alethic modality would take an adverb like "readily."

17  Kalb and Kalb (1974, p.400).

18  All right, just fat.