I think duality serves two purposes:
1) the material which is processed to expand the content of a function
2) due to 1), a determinant of attention given.
If I want to put together a Ti structure, then I will need to make connections between objects. To make these connections I need six things: 1) to signal (+Fe) between the objects that I want to connect; 2) to know what either object wants (+Fi) so as to facilitate the acceptance (-Fe) of their mutual connection; 3) the impartation of a constant flow (Te) of signals between the objects, so that a change in the relations of one will mean a change in the relations of another (thus creating a cause-effect relationship); 4) the imposition of a regulatory mechanism (-Fi) that restrains the objects from interacting with objects outside of the pair and possibly breaking the bond.
Before anything else happens, one must assume that there is a signal and acceptance of the same; otherwise there is no medium across which the signal may propogate. We say that the cause of an electromagnet is the exchange of electrons between poles. The substance of that relationship, therefore, is a constant exchange of Fe aspects. (electrons) The effect is magnetism, a connection between the two poles. When there exists a steady flow of energy between two objects, we say they are connected.
In general, we can say that a given aspect exists as a factor of its dual. It is important to note that an aspects can exist as a factor of an aspect dual to it, but the dual aspect need not exist due to the aspect it factors.
An electromagnetic field exists due to the exchange of electrons between poles of a conductive substance. The exchange of electrons within the field, although invariably an effect of magnetism, need not be stimulated due to the same electromagnetic field, however. (although the field can impede the exchange)