conceptually vague notion of ‘shared information’. We will discuss in what sense humans share information, and to what extent they share information about the information they share. All humans live in the same physical world. We are all engaged in a lifetime’s enterprise of deriving information from this common environment and construct-ing the best possible mental representation of it. We do not all construct the same representation, because of differences in our narrower physical environments on the one hand, and in our cognitive abilities on the other. Perceptual abilities vary in effectiveness from one individual to another. Inferential abilities also vary, and not just in effectiveness. People speak different languages, they have mastered dif-ferent concepts; as a result, they can construct different representations and make different inferences. They have different memories, too, different theories that they bring to bear on their experience in different ways. Hence, even if they all shared the same narrow physical environment, what we propose to call their cognitive environments would still differ. To introduce the notion of a cognitive environment, let us consider a parallel case. One human cognitive ability is sight. With respect to sight, each individual is in a visual environment which can be characterised as the set of all phenomena visible to him. What is visible to him is a function both of his physical environ-ment and of his visual abilities. In studying communication, we are interested in conceptual cognitive abilities. We want to suggest that what visible phenomena are for visual cognition, mani-fest facts are for conceptual cognition. Let us define:

DOI link for conceptually vague notion of ‘shared information’. We will discuss in what sense humans share information, and to what extent they share information about the information they share. All humans live in the same physical world. We are all engaged in a lifetime’s enterprise of deriving information from this common environment and construct-ing the best possible mental representation of it. We do not all construct the same representation, because of differences in our narrower physical environments on the one hand, and in our cognitive abilities on the other. Perceptual abilities vary in effectiveness from one individual to another. Inferential abilities also vary, and not just in effectiveness. People speak different languages, they have mastered dif-ferent concepts; as a result, they can construct different representations and make different inferences. They have different memories, too, different theories that they bring to bear on their experience in different ways. Hence, even if they all shared the same narrow physical environment, what we propose to call their cognitive environments would still differ. To introduce the notion of a cognitive environment, let us consider a parallel case. One human cognitive ability is sight. With respect to sight, each individual is in a visual environment which can be characterised as the set of all phenomena visible to him. What is visible to him is a function both of his physical environ-ment and of his visual abilities. In studying communication, we are interested in conceptual cognitive abilities. We want to suggest that what visible phenomena are for visual cognition, mani-fest facts are for conceptual cognition. Let us define:

conceptually vague notion of ‘shared information’. We will discuss in what sense humans share information, and to what extent they share information about the information they share. All humans live in the same physical world. We are all engaged in a lifetime’s enterprise of deriving information from this common environment and construct-ing the best possible mental representation of it. We do not all construct the same representation, because of differences in our narrower physical environments on the one hand, and in our cognitive abilities on the other. Perceptual abilities vary in effectiveness from one individual to another. Inferential abilities also vary, and not just in effectiveness. People speak different languages, they have mastered dif-ferent concepts; as a result, they can construct different representations and make different inferences. They have different memories, too, different theories that they bring to bear on their experience in different ways. Hence, even if they all shared the same narrow physical environment, what we propose to call their cognitive environments would still differ. To introduce the notion of a cognitive environment, let us consider a parallel case. One human cognitive ability is sight. With respect to sight, each individual is in a visual environment which can be characterised as the set of all phenomena visible to him. What is visible to him is a function both of his physical environ-ment and of his visual abilities. In studying communication, we are interested in conceptual cognitive abilities. We want to suggest that what visible phenomena are for visual cognition, mani-fest facts are for conceptual cognition. Let us define: