-------------------- 16f. What is a fact? -------------------- In discussion on sci.physics.research, one often finds very good information, but also often poor and misleading information. How to distinguish the good from the poor? Everything called knowledge is in fact a set of beliefs of the person claiming it. And this set of beliefs is more or less close to the objective truth, depending on the standards of that persons. Calling so-called knowledge a set of beliefs does not contradict the objectivity of mathematical definitions. When I say that a Banach space is a normed, complete vector space, I both state my belief and happen to coincide with the social consensus of the guild of mathematicians. And when I say that state reduction is a physical process, I both state my belief and happen to coincide with famous physicists like von Neumann and many others, and this is good enough to make this statement honestly, since the community has not reached an agreement on the matter. Telling others what one thinks is true in no way manipulates others any more than feeding others what one thinks is nourishing. But as we shouldn't accept being fed by those with poor judgment about food, we shouldn't accept an opinion for the truth if offered by someone with poor judgment about the relevant areas. It is obvious that whatever a person claims is first and foremost his or her personal opinion, and not a fact. Who takes it for a fact is simply misleading himself or herself. Thus there is no need to qualify each of one's statements by clumsy phrases like 'in my opinion', or 'according to what I have read/understood', or 'as far as I am informed' or 'since this makes most sense to me'. These phrases accompany silently any statement by anyone. It is also obvious that an opinion doesn't become a fact because it is believed by half the number of people from a particular ensemble; truth would otherwise become dependent on the choice of this ensemble. Thus one needs to check the claims, to listen to different sides of a controversy, to ask for sources or justification of an opinion. In this way, anyone who wants to get a clear picture soon notices which claims are trustworthy, which ones are tenable but somewhat shaky, and which ones are poorly founded. On the other hand, in participating in a discussion, honesty only requires that one asserts what one thinks is true, and gives one's reasons upon request. This is the scientific approach, since it lets others check upon the trustworthiness of a claim.