Dummett argued that practical ability is knowledge if and only if having an ability is described as knowing some propositions. He asserts that the ability to speak a language is knowledge itself, because we cannot attempt to speak a language unless we can speak the language. However, it is not clear why such an ability is knowledge itself. In this study, we reinforce his argument by defining knowledge of how to do things as knowledge based on learning experience. We cannot speak a language without learning experience. Moreover, if one gains an ability through learning experience, this means that he at least knows some propositions.
It has been common to formalize counterfactuals (or subjunctive conditionals) in natural language in terms of a certain binary sentential connective, as in Stalnaker  and D. Lewis . This paper suggests that another formalization by means of unary multi-modal operators is natural and appropriate for some counterfactuals. To see this naturalness and appropriateness, we observe an instance of transitive inference constituted of three counterfactuals in natural language, and formalize it by using expressive power of multi-modal logic, in particular Hennessy-Milner logic(HML) and Dynamic logic (DL). As a result, the instance of transitive inference turns out to be justified by the multi-modalized version of the most fundamental and familiar rules of modal logic, that is, the necessitation rule (NAct) and the axiom (KAct).
In speech act theory, there are two typical views about illocutionary acts. According to the conventionalism, they are essentially governed by conventions or the like. According to the dichotomous view, some of them (such as naming a ship) are so but the others (such as asserting) should be analyzed along the line of Griceʼs analysis of nonnatural meaning. However, it seems that both of the views have problems. I will attempt to analyze illocutionary acts on the basis of the two concepts of “socially regarded" and “ostensible attitudes". It appears that various difficulties with existing views can be resolved by such an analysis.
A commonly shared image of convergence is that of arrays of light aiming at a focus―a projected vanishing-point to which all empirical inquiry strives to converge or the Kantian regulative ideal that reason aims at beyond the boundaries of all possible experience. Such an intuitive image of convergence is not completely foreign to Peirce's view, but a predominantly optical model of convergence fails to capture the generality and flexibility of the idea that Peirce wished to advocate. This paper formulates Peirce's convergence theory of truth based upon his mathematical insights and examines a number of criticisms leveled against the theory including that of Quine. I argue that Peirce's understanding of convergence is far more sophisticated than what critics have often assumed and that simultaneous convergence to multiple elements is not excluded from his picture.