Page:Russell - The Problems of Philosophy, 1912.djvu/78

74 possible. Thus the sense-data which make up the appearance of my table are things with which I have acquaintance, things immediately known to me just as they are.

My knowledge of the table as a physical object, on the contrary, is not direct knowledge. Such as it is, it is obtained through acquaintance with the sense-data that make up the appearance of the table. We have seen that it is possible, without absurdity, to doubt whether there is a table at all, whereas it is not possible to doubt the sense-data. My knowledge of the table is of the kind which we shall call "knowledge by description." The table is "the physical object which causes such-and-such sense-data." This describes the table by means of the sense-data. In order to know anything at all about the table, we must know truths connecting it with things with which we have acquaintance: we must know that "such-and-such sense-data are caused by a physical object." There is no state of mind in which we are directly aware of the table; all our knowledge of the table is really knowledge of