The epistemic interpretation of modality is concerned with the knowledge of the speaker or hearer about the world he lives in. This knowledge is usually represented by the set of epistemically possible worlds, i.e. such worlds about which it is not excluded by what the speaker (or hearer) knows that they are the real world. As Lewis put it:
“The content of someone’s knowledge of the world is given by his class of epistemically accessible worlds. These are the worlds that might, for all he knows, be his world; world W is one of them iff he knows nothing, either explicitly or implicitly, to rule out the hypothesis that W is the world where he lives. […] Whatever is true at some epistemically […] accessible world is epistemically […] possible for him. It might be true, for all he knows […]. He does not know […] it to be false. Whatever is true throughout the epistemically […] accessible worlds is epistemically […] necessary; which is to say that he knows […] it, perhaps explicitly or perhaps only implicitly.” (Lewis 1986, p. 27)
Thus, according to the epistemic interpretation of modality, an utterance such as “φ might be the case” is true if and only if the truth of φ is not excluded by what the speaker (or hearer) knows in the moment of the utterance (DeRose 1991; von Fintel and Gillies 2008, 2011; MacFarlane 2011 or Kment 2012). In effect, the modality is relativized to the knowledge of a person or a group relevant in a context; usually it is relativized to the speaker. This relativisation is typically represented by an information base, also called a modal base (MB):
Definition 1 (epistemic possibility I) [von Fintel and Gillies 2008]
MightMB φ is true in w iff φ is true in some world that is MB-accessible from w
MB represents the relevant state of knowledge and MB-accessibility means consistence with this knowledge, so MB–accessibility is a kind of accessibility function between possible worlds. Thus, when I utter the sentence ‘Peter might still be at home’ I do not express the trivial proposition to the effect that there exists a metaphysically possible world in which Peter is now still at home, which is always true as far as contingent facts are concerned. I rather express a proposition comprising epistemic possibility: ‘From what I know it is not excluded that Peter is still at home’. So it might seem that the basic difference between metaphysical and epistemic modality is that when we know that φ is true, ‘Might ¬φ’ may only be interpreted metaphysically (as true); i.e. our knowledge that φ entails the falsity of ‘Might ¬φ’, if the modality is interpreted as epistemic.Footnote 5
We should remember, however, that epistemic modality is relativized to the relevant state of knowledge and this does not always have to be the knowledge of the speaker—it may be the knowledge of the speaker or the hearer, or of both of them considered as a group (see DeRose 1991; MacFarlane 2011; von Fintel and Gillies 2011; Kijania-Placek 2012a). This intuitive difference between epistemic and metaphysical modality might thus require refinement. But in any case, the epistemic possibility must be consistent with some such knowledge state.
The definition of epistemic possibility formulated above (Definition 1) is, however, not directly applicable to example (2), because the sentence is not in the indicative (‘I might be a communist’) but in the subjunctive mode (‘I might have been a communist’). DeRose (1991) warns us against interpreting possibility in the subjunctive mode as epistemic, but already Hacking (1967) had argued against a simple identification of the subjunctive mode with metaphysical modality. von Fintel and Gillies (2008, p. 34) give compelling examples of epistemic modality in the subjunctive mode:
There must have been a power outage overnight
There might have been a power outage overnight
If the modality in (3) were to be interpreted metaphysically, we would attribute metaphysical necessity to this event, while we rather claim that for what we know it looks like there was a power outage overnight (or: the evidence shows conclusively that there have been a power outage overnight).
Modal sentences in subjunctive mode are thus ambiguous and the ambiguity may be considered as the structural ambiguity of scope between the modal operator and the past tense operator. I will use Condoravdi’s example to illustrate this ambiguity:
He might have won the game
He might have (already) won the game. [#but he didn’t]
At that point he might (still) have won the game but he didn’t in the end.
In the epistemic reading, the possibility is from the perspective of the present about the past […]. The modality is epistemic: (6a) is used to communicate that we may now be located in a world whose past includes an event of his winning the game. The possibility is in view of the epistemic state of the speaker: his having won the game is consistent with the information available to the speaker. The issue of whether he won or not is actually settled, but the speaker does not […] know which way it was settled. The counterfactual reading involves a future possibility in the past and the modality is metaphysical. (6b) is used to communicate that we are now located in a world whose past included the (unactualized) possibility of his winning the game.” (Condoravdi 2002, p. 62).
According to Condoravdi, the epistemic modality always takes a wide scope with respect to the operator of the past. The truth conditions of (5), with modality interpreted as epistemic, can thus be defined according to the following schema:
Definition 2 (epistemic modality II) [Condoravdi 2002, p. 61]
φ is true in 〈w, t〉 iff there exist w′, t′ such that w′ ∈ MB (w, t), t′ ≺ t and φ is true in 〈w′, t′〉.
Thus, according to Definition 2, we consider here the possibility about the past, from the point of view of the moment of utterance, because it is the knowledge state from the moment of utterance that is relevant, not the knowledge state form the past: ‘According to what we know now, he might have won the game’.Footnote 6
The metaphysical interpretation of possibility, on the other hand, may be defined thus:
Definition 3 (metaphysical modality) [Condoravdi 2002, p. 63]
φ is true in 〈w, t〉 iff there exist w′, t′, t″ such that t′ ≺ t, w′ ∈ MB (w, t′), t′ ≺ t″ and φ is true in 〈w′, t″〉.
Here we consider what has been true in the past and this is represented by the relativisation of the possibility to the state of knowledge at a moment in the past and not at the moment of utterance. According to Condoravdi, epistemic modality always scopes over the past operator: it is now possible, i.e. not excluded by what we now know, that it has been the case that φ.
Under the assumption of the mandatory wide scope of the modal operator, Fernando (2005) claims that the epistemic interpretation excludes the sustainability of the modal claim if we know that the embedded sentence is not true. So, although ‘John might have won’ may be interpreted as an epistemic possibility, ‘John did not win but he might have won’ allows only a metaphysical interpretation: ‘He might have won, had he listened to my advice. It was within his reach up to some point in time’. This particular example about John is quite convincing and seems to undermine the feasibility of the epistemic interpretation of the possibility in (2). After all, since the Indonesian claims that he is not a communist, his next utterance should not be interpreted as a claim of ignorance. We should remember though, that the inconsistency of claiming that ¬φ followed by ‘It might have been that φ’, where the modal is interpreted as epistemic, is based on the assumption that the knowledge state is relativized to the moment of utterance (the wide scope assumption). After the speaker said that he is not a communist, both the speaker and the hearer know that he is not a communist.
Condoravdi’s thesis (assumed by others as well)—that epistemic modality always takes the wide scope with respect to the operator of the past—has been challenged by von Fintel and Gillies (2008, p. 43), with the help of the following example:
The keys might have been in the drawer
The authors do not give a detailed analysis of this example but claim that here the modality is in the scope of the tense operator. Portner proposes interpreting this case in the following way:
“This sentence has a meaning close to “Based on the evidence that I had in the past, it was possible that the keys were in the drawer.” (It also has a meaning with the expected scope, “Based on the evidence I have now, it is possible that the keys were in the drawer.”)” (Portner 2009, p. 169).
As I may now know something I did not know before, it is clear that these two interpretations give different truth-conditions. It is less clear, however, what are the circumstances that would make the first interpretation more salient. The situation changes if instead of considering the knowledge of the speaker, as Portner does, we concentrate on the knowledge of the hearer. Imagine John and Paul quarreling about who is responsible for losing the keys they have been trying to locate for the last few days. Assume it is Paul who gave away for scrap a metal desk without first checking what was in its drawers. John, irritated, might say:
Many valuable things might have been there. The keys might have been in the drawer. You should have checked
A natural reading of this utterance is based on their mutual knowledge at the moment of utterance: ‘From what we know it is not excluded that the keys were in the drawer’. But assume that the keys are found. Still, it seems that John may sustain his claim:
Anyhow, the keys might have been in the drawer. You should have checked
Now we cannot assume that the possibility is relativized to their knowledge from the moment of utterance, because “Based on the evidence I have now, it is possible that the keys were in the drawer” is incompatible with the fact that the keys are found, so they both now know that the keys haven’t been in the drawer. Yet, John’s utterance may be interpreted as a reproach: ‘The keys weren’t in the drawer. But you didn’t know it, so you should have checked’. This interpretation requires, however, a clear reference to the knowledge of the hearer at a moment in the past, so the possibility is indeed in the scope of the operator of the past tense. And this interpretation of epistemic modality is not excluded by the fact that we now know that something is not the case. Thus the alleged difference between the metaphysical and epistemic possibility—that when we know that φ is true, ‘Might ¬φ’ may only be interpreted metaphysically—turns out not to be sustainable.