The ampersand is an indeterminate missing element game. It relies primarily on the interactions between elements to give the user clues as to the nature of the missing element. Because that element is indeterminate, there is no "true" missing element, merely the possibility of one existing. The ampersand is normally abstract and conceptual.
The traditional definition of the ampersand describes its "emergent" character. The interactions of the elements within the environment seem to describe a new thing, to create something that is "more than the sum of the parts." It is described as the "place between," and the "border."
"Border condition." -- The interface between two complex, yet distinct, elements (such as a house and the street), where the space between is the ampersand, and different from both, it is the relationship.
"Halo condition." -- Two almost identical objects are merged, their "halo" of differences, or the collection as a whole (the relationship between the elements) is the ampersand. The merging can include intellectual merging through similarity. Can be seen as "multivalence," the possibility of multiple values for the elements. The user is able to understand the extra as a thing beyond the "core." The difference is a thing separate from the commonalties. Two elements that are almost identical. Their differences don't fit in the "centre" that is the two elements, nor do they fit into each other. As we increase the number of elements, we develop a "core" that is "similarity," and a "halo" that is difference. The ampersand can be just the "halo," or the whole of the condition (halo and core).
"Dialectic condition." -- Two seemingly mutually exclusive elements become encased in a higher-level understanding of their characters and conditions.