matter has no importance for us, provided it exists even if we cannot know that it exists. We can, obviously, suspect that it may exist, and wonder whether it does; hence it is connected with our desire for knowledge, and has the importance of either satisfying or thwarting this desire.
Again, it is by no means a truism, and is in fact false, that we cannot know that anything exists which we do not know. The word “know” is here used in two different senses. (1) In its first use it is applicable to the sort of knowledge which is opposed to error, the sense in which what we know is true , the sense which applies to our beliefs and convictions, i.e. to what are called judgements . In this sense of the word we know that something is the case. This sort of knowledge may be described as knowledge of truths . (2) In the second use of the word “know” above, the word applies to our knowledge of things , which we may call “acquaintance.” This 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.)