SENSATION GIVES US OUR WORLD OF QUALITIES.--In actual experience sensations are never known apart from the objects to which they belong. This is to say that when we see _yellow_ or _red_ it is always in connection with some surface, or object; when we taste _sour_, this quality belongs to some substance, and so on with all the senses. Yet by sensation we mean only _the simple qualities of objects known in consciousness as the result of appropriate stimuli applied to end-organs_. We shall later see how by perception these qualities fuse or combine to form objects, but in the present chapter we shall be concerned with the qualities only. Sensations are, then, the simplest and most elementary knowledge we may get from the physical world,--the red, the blue, the bitter, the cold, the fragrant, and whatever other qualities may belong to the external world. We shall not for the present be concerned with the objects or sources from which the qualities may come. To quote James on the meaning of sensation: "All we can say on this point is that _what we mean by sensations are first things in the way of consciousness_. They are the _immediate_ results upon consciousness of nerve currents as they enter the brain, and before they have awakened any suggestions or associations with past experience. But it is obvious that _such immediate sensations can be realized only in the earliest days of life_." THE ATTRIBUTES OF SENSATION.--Sensations differ from each other in at least four respects; namely, _quality_, _intensity_, _extensity_, and _duration_. It is a difference in _quality_ that makes us say, "This paper is red, and that, blue; this liquid is sweet, and that, sour." Differences in quality are therefore fundamental differences in _kind_. Besides the quality-differences that exist within the same general field, as of taste or vision, it is evident that there is a still more fundamental difference existing between the various fields. One can, for example, compare red with blue or sweet with sour, and tell which quality he prefers. But let him try to compare red with sweet, or blue with sour, and the quality-difference is so profound that there seems to be no basis for comparison.