in a cognitive environment if the environment provides sufficient evidence for its adoption, and as we all know, mistaken assumptions are sometimes very well evidenced. Anything that can be seen at all is visible, but some things are much more visible than others. Similarly, we have defined ‘manifest’ so that any assumption that an individual is capable of constructing and accepting as true or probably true is manifest to him. We also want to say that manifest assumptions which are more likely to be entertained are more manifest. Which assumptions are more manifest to an individual during a given period or at a given moment is again a function of his physical environment on the one hand and his cognitive abilities on the other. Human cognitive organisation makes certain types of phenomena (i.e. perceptible objects or events) particularly salient. For instance, the noise of an explosion or a doorbell ringing is highly salient, a background buzz or a ticking clock much less so. When a phenomenon is noticed, some assumptions about it are standardly more accessible than others. In an environment where the doorbell has just rung, it will normally be strongly manifest that there is someone at the door, less strongly so that whoever is at the door is tall enough to reach the bell, and less strongly still that the bell has not been stolen. The most strongly manifest assumption of all is the assumption that the doorbell has just rung, the evidence for which is both salient and conclusive. We will have more to say, in chapter 3, about the factors which make some assumptions more manifest than others in a given situ-ation. For the moment it is the fact rather than the explanation that matters. Our notion of what is manifest to an individual is clearly weaker than the notion of what is actually known or assumed. A fact can be manifest without being known; all the individual’s actual assumptions are manifest to him, but many more assumptions which he has not actually made are manifest to him too. This is so however weakly the terms ‘knowledge’ and ‘assumption’ are construed. In a strong sense, to know some fact involves having a mental representation of it. In a weaker sense, to say that an individual knows some fact is not necessarily to imply that he has ever entertained a mental representation of it. For instance, before read-ing this sentence you all knew, in that weak sense, that Noam Chomsky never had breakfast with Julius Caesar, although until now the thought of it had never crossed your mind. It is generally accepted that people have not only the know-ledge that they actually entertain, but also the knowledge that they are capable of deducing from the knowledge that they entertain. However, something can be manifest without being known, even in this virtual way, if only because some-thing can be manifest and false, whereas nothing can be known and false. Can something be manifest without being actually assumed? The answer must again be yes. Assumptions are unlike knowledge in that they need not be true. As with knowledge, people can be said to assume, in a weak sense, what they are capable of deducing from what they assume. However, people do not assume, in any sense, what they are merely capable of inferring non-demonstratively – that is, by some creative process of hypothesis formation and confirmation – from what they assume. Although it presumably followed non-demonstratively from what you