Kant's First Analogy: The Permanence Of Substance In Space And Time It's not 'all in your head.' Thus Kant would assure the discriminating philosophy student that merely because he or she might perceive an object in a certain fashion does not mean that the object is, in actual fact, true to the observer's mental apprehension of the object. Despite attempts by some of his contemporaries to deny the reality of material existence, Kant instead proposed that material objects had an external reality in space and time that was 'real' beyond the images they presented to the human observer's mind. Reality had an existence in space and time beyond psychological perceptions of the observer.

Thus, Kant's first analogy states that all through all possible changes of an object's appearances, the essential substance of a 'thing' persists, even if the observer has an optical illusion to the contrary. The object's essential substance is neither increased nor diminished in nature, even if the observer may perceive this fact to be the case. This is because all appearances are in time and space for Kant, even if we may perceive them differently -- thus, merely because I perceive a girl to look older because she is dressed differently, because she entered her bedroom in sweats, and then exited it in a cocktail dress and makeup, does not mean that she has suddenly aged more than her sister, who is still in the same childish clothing. Nor does it mean that the girl is not real, or only real as a young woman, so long as she had an existence in my mind as a young woman...

For Kant, as this person still occupies the same time and space, regardless of her appearing to my apprehension as different, she is still the same person.
Kant's assertion stands as a kind of refutation of a radical empiricism, that one can make no general principles about life on a predictable basis -- in other words, that simply because I see someone today in a certain fashion does not mean that that person will appear to be the same tomorrow -- but the object of my gaze is still the same person, even if I may feel differently about that person, and see the person as different. Kant suggests that even when something appears to change it is still retains the same essence, even while it is affected by the perceptions of the observer and even while it appears differently to the observer.

To take another example of a shock of appearances, consider the surprise a young child occasionally feels when he or she sees his or her teacher in the supermarket, dressed in ordinary clothes, and no longer in a position of authority. The teacher may seem like a different person, but the only thing that has changed are the perceptions in the mind of the child. This change occurred because of the child's perception of the teacher, because of a change of circumstance, and a change of the teacher's temporary and alterable appearance, not because the teacher has changed. Rather, although details may have conspired to create this altered perception, the 'thing' or teacher still sees him or herself as the same entity…