我們似乎都同意，許多事情是有其它的可能性（例如，蘇格拉底有可能長得高一些、我的桌子有可能更大一些、等等）。我們似乎也會同意，有一些事情是必然的而非偶然的（例如：蘇格拉底必然是人、水必然是H2O、等等）。這些事情，主要是關於「可能性」與「必然性」的，而不是關於這個經驗世界發生的事，我們稱之為「模態」事實。問題是，如果模態事實在某意義上超出了這個經驗世界，我們要如何能夠對它們擁有知識，要如何能夠證成我們對它們的信念呢？

這個問題，在近年的文獻中已受到廣泛的討論。例如，「模態懷疑論」的回答，是直接否認我們可以對模態事實擁有知識。而「模態理性論」則是主張我們具有某種特殊的認知官能（如「直覺」），可以幫助我們接觸到模態真理。此外還有「反事實理論」，試圖在不引入直覺這類特殊官能的情況下，將我們的模態知識立基在我們對反事實條件句的知識上。其他的理論則是試圖找尋各種不同的基礎來解釋模態知識，像是可設想性、想像力、語言能力、等等。

在本課程中，我們將仔細研讀關於模態知識論的討論。我們會特別集中在最近幾年當中，相關文獻的發展和趨勢。從這個角度來看，有兩本論文集會十分有幫助：(1) Synthese即將出版、以「New Directions in the Epistemology of Modality」為題的專刊；(2) 2017年Synthese Library出版的專刊「Modal Epistemology After Rationalism」。此外, 我們也會閱讀一些關於模態知識論的經典文獻。

We all agree that some things might have been otherwise than they are (e.g. that Socrates might have been taller, that my desk might have been larger, etc.). We also seem to agree that some things hold necessarily rather than accidentally (e.g. that Socrates is essentially a man, that water is necessarily H2O, etc.). These are called ‘modal’ facts, which concern what is possible and what is necessary, rather than how things actually are in the empirical world. Now, the crucial question is, How can we have any knowledge or justification of such modal facts, if they are in some sense beyond the actual world?

There have been many attempts in the literature to answer this question. Modal scepticism answers it by directly denying that we can really have knowledge of the modal facts. Modal rationalism, by contrast, claims that we have a special cognitive faculty (e.g. ‘intuition’) by which we may access modal truths. The counterfactual accounts propose to ground our modal knowledge on our knowledge of counterfactual conditionals without appealing to the special faculty of intuition. There are a variety of further accounts, invoking conceivability, imagination, semantic competence, etc.

In this course, we will study the epistemology of modality in some detail. We will especially focus on the recent development in the relevant literature. In this connection, two collections of papers are quite useful: (i) A special issue of Synthese entitled ‘New Directions in the Epistemology of Modality’ (forthcoming), and (ii) Fischer and Leon (eds.) (2017), Modal Epistemology After Rationalism, Synthese Library, Springer. But in addition to this, we will also go through some of the classics in the literature on modal epistemology.