Some are dualists, puzzled how the One (usually Mind or the Ideal) can possibly interact with the Many (the Body or the Material World). There are other kinds of dualists, those thinking the world divides into forces of good and evil, for example, but the idealism/materialism divide has a long history in philosophy under dozens of different names through the ages.

Many philosphers prefer triads, triplicities, or trinities as their fundamental structures, and in these we may find the most sensible way to divide the world as we know it into "worlds," realms, or orders.

Those who divide their philosophy into four usually arrange it two by two (Schopenhauer, Heidegger, Derrida - in jest). There are a few who think a pentad has explanatory power. Another handful look to the mystical seven (the number of planets and thus days) for understanding.

Since the Pythagoreans drew their triangular diagram of the tetractus, ten has been a divine number for some. Aristotle found ten categories. The neo-Platonist Kabalists have ten sephiroth.

The most important philosopher since Aristotle, Immanuel Kant, structured his architectonic into twelve categories, arranged four by three.

We will scrutinize these architectures to see if the various thinkers divide their worlds the same way, whatever they call their divisions. We'll see that there is a surprising amount of agreement among them, especially considering their disagreements on terminology.