When Hume examined, with more and more minuteness, the elements of the materials on which the mind works, he could still find nothing but these impressions and ideas. Looking at language as a machinery for giving expression to thought, he thus established for himself a test of its adaptation to its right use,--a test for discovering whether in any given case it really served the purpose of language, or was a mere unmeaning sound. As he found that there was nothing on which thought could operate but the impressions received through sensation, or the ideas left by them, he considered that a word which had not a meaning to be found in either of these things, had no meaning at all. He looked upon ideas as the goods with which the mind was stored; and on these stores, as being of the character of impressions, while they were in the state of coming into the mind. When any one, then, in reasoning, or any other kind of literature, spoke of any thing as existing, the principle of his theory was, that this storehouse of idealized impressions should be searched for one corresponding to the term made use of. If such an impression were not found, the word was, so far as our human faculties were concerned, an unmeaning one. Whether there was any existence corresponding to its meaning, no one could say: all that the sceptical philosopher could decide was, that, so far as human intellect was put in possession of materials for thought, it had nothing to warrant it in saying, that this word represented any thing of which that intellect had cognizance.