Sensations, then, first make us acquainted with innumerable things, and then are replaced by thoughts which know the same things in altogether other ways. And Locke's main doctrine remains eternally true, however hazy some of his language may have been, that "though there be a great number of considerations wherein things may be compared one with another, and so a multitude of relations; yet they all _terminate in_, and are concerned about, those simple ideas[6] either of sensation or reflection, which I think to be the whole materials of all our knowledge.... The simple ideas we receive from sensation and reflection are the _boundaries_ of our thoughts; beyond which, the mind whatever efforts it would make, is not able to advance one jot; nor can it make any discoveries when it would pry into the nature and hidden causes of those ideas."[7] The nature and hidden causes of ideas will never be unravelled till the _nexus_ between the brain and consciousness is cleared up. All we can say now is that sensations are _first_ things in the way of consciousness. Before conceptions can come, sensations must have come; but before sensations come, no psychic fact need have existed, a nerve-current is enough. If the nerve-current be not given, nothing else will take its place. To quote the good Locke again: "It is not in the power of the most exalted wit or enlarged understanding, by any quickness or variety of thoughts, to invent or frame one new simple idea [i.e. sensation] in the mind.... I would have any one try to fancy any taste which had never affected his palate, or frame the idea of a scent he had never smelt; and when he can do this, I will also conclude that a blind man hath ideas of colors, and a deaf man true distinct notions of sounds."[8] The brain is so made that all currents in it run one way. Consciousness of some sort goes with all the currents, but it is only when new currents are entering that it has the sensational _tang_. And it is only then that consciousness directly _encounters_ (to use a word of Mr. Bradley's) a reality outside itself.