(from Chap.2 Upadesa Sahasri)
51. The disciple said, Though eternal, I am not the Supreme Self. My Nature is one of transmigratory existence consisting of agency and experiencing of its results, as it is known by evidences such as sense-perception etc. It is not due to Ignorance. For it cannot have the innermost Self for its object. Ignorance consists of the superimposition of the qualities of one thing on another e.g., well-known silver on well-known mother-of-pearl or a well-known human being on a (well-known) trunk of a tree and vice versa. An unknown thing cannot be superimposed on a known one and vice versa. The non-Self cannot be superimposed on the Self, for It is not known. Similarly, the Self cannot be superimposed on the non-Self for the very same reason.
Here is kernel of the problem with using analogies. They can be mistakenly understood in two ways. (I’d love to be able to find three ways to conform to standard philosophical practice) First there is the error of misconstruing what the element is that you are attempting to offer an analogy for and second the tendency to overgeneralize the point of the analogy i.e. to turn an analogy into an homology. So we can take the superimposition analogy to be about error or scepticism or belief and get sidetracked into the interesting but irrelevant to the purpose of the analogy, ways of establishing veridical knowledge or the status of the ‘false’ object etc.
The disciple here is making the over generalization error. He views the template of their having to be two separate and separable things as the fixed nature of superimposition. In fact as a teaching strategy the introduction to the advaitin concept via a graduated explication is an excellent one similar to the adhiropa/apavada device. It’s a two stage rocket!