真理条件から知識条件へ
水本正晴（Masaharu Mizumoto）
北陸先端科学技術大学院大学
Take Williamson’s famous knowledge account of assertion literally, then we obtain thefollowing instances of the schema;
1) Assert “If P, then Q” only if you know that if P, then Q.
2) Assert “P but Q” only if you know that P but Q.
But what kind of knowledge is it, which appears in these sentences? Is there suchknowledge at all? In this paper I will argue that there is indeed such knowledge, andeven try to explain the content of the assertion in terms of the content of suchknowledge, which I call knowledge-condition.
Here knowledge is understood as belief that is monotonic against informationin the environment, in the sense of surviving the reception of any information in theactual world at a particular time, or what I called the sustainable belief (Mizumoto2011). Given this understanding, we may explain the content of the assertion in thefollowing way;(KC) By her assertion “P” A means what A believes when and only when A knows thatP, relative to A’s actual informational state. 1
In contrast with simple “’P’ means that P”, which is about the meaning of sentence
independent of the speaker, KC explicitly refers to the speaker, explaining her
meaning by the content of (possible) knowledge. Here the content of belief isindividuated by the possible belief change of the speaker, which will allow us to havethe content of knowledge that is finer-grained than the standard truth-condition.
Thus in the case of 1), the semantic content of A’s assertion “If P, then Q” isexplained by A’s knowledge that if P, then Q, which is then explained by A’s sustainable
belief that if P, then Q. 2 This means that, there is no information in the environment
The obvious assumption here is that the content of knowledge is more basic thanthat of belief, even if knowledge is analyzed by belief. As Williamson says, belief may
be “botched knowledge”. Indeed, I hold that knowledge be more primitive than truth.
2We assume here, unlike popular probabilistic analyses of indicatives, that the beliefof such indicative conditionals is a full belief, since we believe that Modus Ponens isessential to any conditional, while we cannot eliminate the counterexample to MP aslong as we assume such a probabilistic approach (Mizumoto 2009). Our belief about theworld is the sea of full beliefs, with only islands of partial beliefs depending on ourpractical interests.
1such that A would abandon or suspend the belief in question, like information suchthat P but not-Q. Moreover, even if P is not realized, there should be some reason forassuming the connection between P and Q, which may be undermined by someinformation. The knowledge condition then commit the speaker to there being no suchinformation around, and if there is, the world is not like what is asserted, even if thesentence may still be true, which marks the difference between truth condition andknowledge condition (cf. material conditional analysis of the indicatives by Grice andJackson based on conversational / conventional implicature).
In the case of 2), the knowledge that P but Q is likewise explained in terms of
the sustainable belief that P but Q. This kind of belief can be in fact abandoned orsuspended if there is information about the relation between P and Q such that P infact depends on Q, or vice versa. Among such information is that if P, then Q. Givensuch information, even if you still believe both P and Q, you would not believe that P

but Q, any more (cf. cancelability test of implicature). This does not mean, again, that
“P but Q” is false in that situation.
In contrast with the standard explanation in terms of implicature, in whichsuch implicature of an assertion is understood as something over and above the truth
condition of the sentence uttered (the same as that of “Not-P or Q” in the case of 1) and“P and Q” in the case of 2)), our explanation gives the semantic content as a single
unified content. Since in communication what a person means by an utterance is what
she intends the hearer to know, the speaker herself knows what she means by thatutterance. Then the semantic content of A’s assertion, and therefore its knowledge
condition, can be understood as the set of centered worlds in which A knows thecontent (which corresponds to the primary truth condition of Chalmers, but I do nottake it to be a truth condition). I do not however take this as the truth condition, since

it is essential to the explanation of what a person means to eliminate the possibility ofaccidental truth. The gap between the content of a sentence and what is asserted bythat sentence arises from the very possibility of accidental truth. In general, as long as
the content of assertion (or any utterance), or that of belief (intention, desire, fear, etc.),
of a person is explained by truth condition, it can be satisfied in any strange way quite
unexpected by that person (cf. the problem of logical omniscience). But stipulating theexistence of “implicature” here, which is itself explained by the truth condition, would
just carry over the original gap. In contrast, the content of knowledge almost bydefinition eliminates this possibility.
We are not suggesting that the content of knowledge cannot be represented (ifonly derivatively) by truth condition, let alone that truth condition should beabandoned. But we certainly propose to replace the Davidsonian assumption of thealleged essential connection between truth and meaning by that of knowledge andmeaning. We then consider how much this approach can be generalized, and evaluate
it in comparison with cognitive semantics. (なお発表は日本語で行います)