"Hamlet: Do you see yonder cloud that's almost in shape of a camel?
Polonius: By th' Mass, and 'tis like a camel, indeed.
Hamlet: Methinks it is like a weasel.
Polonius: It is backed like a weasel.
Hamlet: Or like a whale.
Polonius: Very like a whale.
Now the whale, the camel, etc., were not in the sky. The clouds are mere aggregates of water-drops. The whale, etc., were in the minds of Hamlet and Polonius. But they could both see the cloud. Thus an image of the cloud was also in their minds, Moreover they knew it to be a cloud. Yet they could "see" animals in it. This is the important fact about mental phenomena. The physical cloud in the sky is just itself, made of water-drops. The mental cloud is multiplicity. To begin with it is a pattern of brain-processes, just as physical as the water-drops. But it is experienced (i) as a could, (ii) as a whale, (iii) as a camel and so on. We cannot dismiss these as "illusions" for it is just the occurrence of such illusions that we seek to explain - besides why is it illusory to see the thing as a whale but not illusory to see it as a cloud? And how did Hamlet know it was "really" a cloud?"
Reference: Learning, Remembering and Knowing - Patrick Meredith