Williamson1主張：(a) 單憑對語義的理解（和概念掌握），哲學家不能獲致任何哲學知識；(b) 但哲學家的確具有一些哲學知識，如形上學模態知識；因而(c)：哲學家獲得哲學知識的方法一定不是單憑語義分析。Williamson認為哲學家獲致哲學知識的方法主要是「想像模擬」的椅驗法。本文說明Williamson上述的論證和看法，也仔細評論(a)。作者認為，Williamson論證(a)的方式（指出理解—同意鍊不必然成立）也可以用來論證想像模擬並非獲得哲學知識的方法。作者進一步主張，在哲學知識獲得上，(i)想像模擬法和意義理解（或概念掌握）法其實一樣可靠；(ii)對一個詞義的理解（或概念掌握）方式其實不只一種，並且允許程度。在此理解下，Williamson的椅驗知識其實只是傳統所謂的先驗知識。

Williamson argues: (a) we (ordinary people and philosophers) gain no philosophical knowledge at all simply on the basis of linguistic and conceptual competence, yet (b) we do have some philosophical knowledge, such as our modal knowledge about certain necessity claims and possibility claims; therefore (c) our philosophical knowledge must come from methods other than linguistic and conceptual competence. He further claims that the most important method used for achieving modal knowledge is through what he calls “imaginative simulation” and that the products of such a process are concrete examples of what he calls “armchair” knowledge which differs both from a priori and from a posteriori knowledge. I explain Williamson’s above argument and his above assertions in details in this paper and focus my criticisms on his (a). I argue that, the way Williamson argues for (a) (by giving examples showing that understanding-assent links do not necessarily hold) can also be exploited to argue for the conclusion that “imaginative simulation” is not the method that philosophers use to gain philosophical modal knowledge. On the question about our methods for pursuing philosophical knowledge, I further argue that (i) the method of simply relying upon our linguistic and conceptual competence is actually as reliable as the method of imaginative simulation, and (ii) there are multiple ways to understand the meaning of a term or to grasp a concept and both understanding and grasping allow degrees. With a suitable understanding about “understanding”, I argue that Williamson’s armchair knowledge is nothing but the a priori knowledge of the good old days philosophy.