The ancient skeptic said to himself: The colors of objects vary according to the light, and according to the position and distance of the objects; can we say that any object has a real color of its own?
A staff stuck into water looks bent, but feels straight to the touch; why believe the testimony of one sense rather than that of another?
Such questionings led to far-reaching consequences.

They resulted in a forlorn distrust of the testimony of the senses, and to a doubt as to our ability to know anything as it really is.
Now, the distinction between appearances and realities exists for us as well as for the ancient skeptic, and without being tempted to make such extravagant statements as that there is no such thing as truth, and that every appearance is as real as any other, we may admit that it is not very easy to see the full significance of the distinction, although we are referring to it constantly.
For example, we look from our window and see, as we say, a tree at a distance.

What we are conscious of is a small bluish patch of color.
Now, a small bluish patch of color is not, strictly speaking, a tree; but for us it represents the tree.

Suppose that we walk toward the tree.

Do we continue to see what we saw before?
Of course, we say that we continue to see the same tree; but it is plain that what we immediately perceive, what is given in consciousness, does not remain the same as we move.