Been using the four corners of the Marseille Tarot card World to explain some metaphysical projects in my classes. These are projects that take the four predicates Universal, Particular, Abstract and Concrete as special features of the world - its four corners. The top left corner, with the angel, points at the abstract, the eagle corner to the universal, the bottom left to the concrete and the bottom right to the particular.
Then we try to make do with less than four corners - making others dispensable. Some classical projects try to ally either both corners on the bottom to make the other two dispensable (the nominalist projects) or the top corners to make the bottom ones dispensable (the bundle-ist project). The general difficulties of these projects lie at trying to get the bottom out of the top and vice-versa. How to get particularity, for example, out of bundles of properties without having to swallow the undesirable consequences of taking indiscernibility to be enough for identity. The problem in this case is really how to build particularity out of any other corner. That stimulates a metaphysics of tropes (or modes) that would take shades of properties to be an ingredient of the world and therefore abstract particulars to be enough to replace universals and concretes. It also stimulates projects to take concrete universals as primitive and get what abstracts provides and take particulars as parts - indiscernible ingredients are not the same, they are part of the same whole.
The exercise is interesting because it tells us something about how the tarot card folds - what can you get with an origami made of the World Marseille card. It reveals how difficult, for instance, it is to get concreteness (in terms of co-presence of tropes of properties) out of the other corners. Even if particulars are taken care of by tropes. Also the abstract is very difficult to make redundant even if properties are taken care by concrete universals. In fact, all corners are equally difficult to dispense, but for very difficult reasons.