That is to say, the desk seen must be in a certain relation to my body, and this body, as I know it, also consists of experiences.

Thus, if I am to know that I see the desk, I must realize that my eyes are open, that the object is in front of me and not behind me, etc.
The desk as seen varies with the relation to the body in certain ways that we regard as natural and explicable.

When I am near it, the visual experience is not just what it is when I recede from it.

But how can I know that I am near the desk or far from it?
What do these expressions mean?
Their full meaning will become clearer in the next chapter, but here I may say that nearness and remoteness must be measured for me in experiences of some sort, or I would never know anything as near to or far from my body.
Thus, all our sensory experiences are experiences that fall into a certain system or order.

It is a system which we all recognize implicitly, for we all reject as merely imaginary those experiences which lack this setting.