series of distinct terms, but in what we know directly there are no clear cut distinctions and so no series. The assumption which we usually make that the facts must consist of such things as events and qualities and material objects is not based upon the evidence of direct knowledge: we make the assumption that the facts must be of this kind simply because they can be explained in these terms. It is true that there is some correspondence between the actual facts and the common sense world of solid tables and so on, and we usually jump to the conclusion that this correspondence would not be possible unless the facts had common qualities. There is no denying that facts can be classified and it seems only natural to take it for granted that whatever can be classified must share some quality with whatever belongs to the same class, that, indeed, it is just on account of all sharing the same common quality that facts can be classified as being all of the same kind. Thus common sense takes it for granted that all facts which can be classified as red, and so explained by all the general laws which we know about the relation of red things to other things, must share a common quality of redness. It seems only natural to make this assumption because we are so used to making it, but if we stop to examine the facts which we know directly we discover that they do not bear it out, and we are gradually driven to the conclusion that it is quite unwarranted. It is only bit by bit, as we gradually accustom ourselves to doubting what we have been accustomed to take for granted, that we realize how ill this assumption fits the facts. CHAPTER II FACT Common sense starts out with the assumption that what we know directly is such things as trees, grass, anger, hope and so on, and that these things have qualities such as solidity, greenness, unpleasantness and so on, which are also facts directly known. It is not very difficult to show that, if we examine the facts which we know directly, we cannot find in them any such things as trees, grass, or minds, over and above the various qualities which we say belong to them. I see one colour and you see another: both of them are colours belonging to the grass but neither of us can find anything among the facts known to him corresponding to this grass, regarded as something over and above its various qualities, to which those qualities are supposed to belong. This drives common sense back unto its second line of defence where it takes up the much stronger position of asserting that, while trees, grass, minds, etc., are not among the facts directly known, their qualities of solidity, greenness, etc., are. It is usual to add that these qualities are signs of real trees, grass, etc., which exist independently but are only known to us through their qualities.