knew and assumed before you read this sentence that Ronald Reagan and Noam Chomsky never played billiards together, this was not, until now, an assumption of yours: it was only an assumption that was manifest to you. Moreover, some-thing can be manifest merely by being perceptible, and without being inferable at all from previously held knowledge and assumptions. A car is audibly passing in the street. You have not yet paid any attention to it, so you have no knowledge of it, no assumptions about it, even in the weakest sense of ‘knowledge’ and ‘assumption’. But the fact that a car is passing in the street is manifest to you. We will now show that because ‘manifest’ is weaker than ‘known’ or ‘assumed’, a notion of mutual manifestness can be developed which does not suffer from the same psychological implausibility as ‘mutual knowledge’ or ‘mutual assumptions’. To the extent that two organisms have the same visual abilities and the same physical environment, the same phenomena are visible to them and they can be said to share a visual environment. Since visual abilities and physical environments are never exactly identical, organisms never share their total visual environments. Moreover, two organisms which share a visual environment need not actually see the same phenomena; they are merely capable of doing so. Similarly, the same facts and assumptions may be manifest in the cognitive environments of two different people. In that case, these cognitive environments intersect, and their intersection is a cognitive environment that these two people share. The total shared cognitive environment of two people is the intersection of their two total cognitive environments: i.e. the set of all facts that are manifest to them both. Clearly, if people share cognitive environments, it is because they share physical environments and have similar cognitive abilities. Since physical envir-onments are never strictly identical, and since cognitive abilities are affected by previously memorised information and thus differ in many respects from one per-son to another, people never share their total cognitive environments. Moreover, to say that two people share a cognitive environment does not imply that they make the same assumptions: merely that they are capable of doing so. One thing that can be manifest in a given cognitive environment is a charac-terisation of the people who have access to it. For instance, every Freemason has access to a number of secret assumptions which include the assumption that all Freemasons have access to these same secret assumptions. In other words, all Freemasons share a cognitive environment which contains the assumption that all Freemasons share this environment. To take another example, Peter and Mary are talking to each other in the same room: they share a cognitive environment which consists of all the facts made manifest to them by their presence in this room. One of these facts is the fact that they share this environment. Any shared cognitive environment in which it is manifest which people share it is what we will call a mutual cognitive environment. In a mutual cognitive environ-ment, for every manifest assumption, the fact that it is manifest to the people who share this environment is itself manifest. In other words, in a mutual cognitive environment, every manifest assumption is what we will call mutually manifest. Consider, for example, a cognitive environment E shared by Peter and Mary, in which (41) and (42) are manifest:

DOI link for knew and assumed before you read this sentence that Ronald Reagan and Noam Chomsky never played billiards together, this was not, until now, an assumption of yours: it was only an assumption that was manifest to you. Moreover, some-thing can be manifest merely by being perceptible, and without being inferable at all from previously held knowledge and assumptions. A car is audibly passing in the street. You have not yet paid any attention to it, so you have no knowledge of it, no assumptions about it, even in the weakest sense of ‘knowledge’ and ‘assumption’. But the fact that a car is passing in the street is manifest to you. We will now show that because ‘manifest’ is weaker than ‘known’ or ‘assumed’, a notion of mutual manifestness can be developed which does not suffer from the same psychological implausibility as ‘mutual knowledge’ or ‘mutual assumptions’. To the extent that two organisms have the same visual abilities and the same physical environment, the same phenomena are visible to them and they can be said to share a visual environment. Since visual abilities and physical environments are never exactly identical, organisms never share their total visual environments. Moreover, two organisms which share a visual environment need not actually see the same phenomena; they are merely capable of doing so. Similarly, the same facts and assumptions may be manifest in the cognitive environments of two different people. In that case, these cognitive environments intersect, and their intersection is a cognitive environment that these two people share. The total shared cognitive environment of two people is the intersection of their two total cognitive environments: i.e. the set of all facts that are manifest to them both. Clearly, if people share cognitive environments, it is because they share physical environments and have similar cognitive abilities. Since physical envir-onments are never strictly identical, and since cognitive abilities are affected by previously memorised information and thus differ in many respects from one per-son to another, people never share their total cognitive environments. Moreover, to say that two people share a cognitive environment does not imply that they make the same assumptions: merely that they are capable of doing so. One thing that can be manifest in a given cognitive environment is a charac-terisation of the people who have access to it. For instance, every Freemason has access to a number of secret assumptions which include the assumption that all Freemasons have access to these same secret assumptions. In other words, all Freemasons share a cognitive environment which contains the assumption that all Freemasons share this environment. To take another example, Peter and Mary are talking to each other in the same room: they share a cognitive environment which consists of all the facts made manifest to them by their presence in this room. One of these facts is the fact that they share this environment. Any shared cognitive environment in which it is manifest which people share it is what we will call a mutual cognitive environment. In a mutual cognitive environ-ment, for every manifest assumption, the fact that it is manifest to the people who share this environment is itself manifest. In other words, in a mutual cognitive environment, every manifest assumption is what we will call mutually manifest. Consider, for example, a cognitive environment E shared by Peter and Mary, in which (41) and (42) are manifest:

knew and assumed before you read this sentence that Ronald Reagan and Noam Chomsky never played billiards together, this was not, until now, an assumption of yours: it was only an assumption that was manifest to you. Moreover, some-thing can be manifest merely by being perceptible, and without being inferable at all from previously held knowledge and assumptions. A car is audibly passing in the street. You have not yet paid any attention to it, so you have no knowledge of it, no assumptions about it, even in the weakest sense of ‘knowledge’ and ‘assumption’. But the fact that a car is passing in the street is manifest to you. We will now show that because ‘manifest’ is weaker than ‘known’ or ‘assumed’, a notion of mutual manifestness can be developed which does not suffer from the same psychological implausibility as ‘mutual knowledge’ or ‘mutual assumptions’. To the extent that two organisms have the same visual abilities and the same physical environment, the same phenomena are visible to them and they can be said to share a visual environment. Since visual abilities and physical environments are never exactly identical, organisms never share their total visual environments. Moreover, two organisms which share a visual environment need not actually see the same phenomena; they are merely capable of doing so. Similarly, the same facts and assumptions may be manifest in the cognitive environments of two different people. In that case, these cognitive environments intersect, and their intersection is a cognitive environment that these two people share. The total shared cognitive environment of two people is the intersection of their two total cognitive environments: i.e. the set of all facts that are manifest to them both. Clearly, if people share cognitive environments, it is because they share physical environments and have similar cognitive abilities. Since physical envir-onments are never strictly identical, and since cognitive abilities are affected by previously memorised information and thus differ in many respects from one per-son to another, people never share their total cognitive environments. Moreover, to say that two people share a cognitive environment does not imply that they make the same assumptions: merely that they are capable of doing so. One thing that can be manifest in a given cognitive environment is a charac-terisation of the people who have access to it. For instance, every Freemason has access to a number of secret assumptions which include the assumption that all Freemasons have access to these same secret assumptions. In other words, all Freemasons share a cognitive environment which contains the assumption that all Freemasons share this environment. To take another example, Peter and Mary are talking to each other in the same room: they share a cognitive environment which consists of all the facts made manifest to them by their presence in this room. One of these facts is the fact that they share this environment. Any shared cognitive environment in which it is manifest which people share it is what we will call a mutual cognitive environment. In a mutual cognitive environ-ment, for every manifest assumption, the fact that it is manifest to the people who share this environment is itself manifest. In other words, in a mutual cognitive environment, every manifest assumption is what we will call mutually manifest. Consider, for example, a cognitive environment E shared by Peter and Mary, in which (41) and (42) are manifest: