is the sense in which we know sense-data. (The distinction involved is roughly that between savoir and connaître in French, or between wissen and kennen in German.)
Thus the statement which seemed like a truism becomes, when re-stated, the following: "We can never truly judge that something with which we are not acquainted exists." This is by no means a truism, but on the contrary a palpable falsehood. I have not the honour to be acquainted with the Emperor of China, but I truly judge that he exists. It may be said, of course, that I judge this because of other people's acquaintance with him. This, however, would be an irrelevant retort, since, if the principle were true, I could not know that any one else is acquainted with him. But further: there is no reason why I should not know of the existence of something with which nobody is acquainted. This point is important, and demands elucidation.
If I am acquainted with a thing which exists, my acquaintance gives me the knowledge that it exists. But it is not true that, conversely, whenever I can know that a
