So the question has often been raised at to why Earth and Stone are separate elements in the context of the BIONICLE story. Now obviously there are separate real life reasons why this is the case, but I intend to take on somewhat of an internal critique and show that, quite plausibly, there is a relevant difference between Earth and Stone (for the purposes of this, we may also assume I’m referring Ice and Water as well).
Ultimately this issue folds down into the ontology of substance. In our own world, there are different view on ontology of substance, or what substance makes up our world. Some people are materialists (physical matter is all that exists), dualists (physical and mental substance exists), or idealists (mental substance exists).
Now when we look at the BIONICLE story, it’s important to trace back to its origin the creation or conceptualization of the original four elements. These fall back to the Greeks and Aristotle, who thought that the world was made of four substances, Earth, Water, Fire, and Air. In other words, the world was fully reducible to these four substances, which we may call Earth, Water, … , Air, and none of these are equal to each other (i.e. Water at its root is not Air, which is not Earth and so on). It is all otherwise some combination of the four. Now, modern philosophers have one of the three views I mentioned above. Many hold to a purely physical ontology, i.e. world is reducible to the physical substance. Now let’s apply this to the BIONICLE universe. For the purposes here, we can say that their world is just made up of many different substances, each of which comprises and element over which a Toa has power. Ultimately each of these substances is fully separate, and not reducible to each other. And so, in the context of BIONICLE, a Stone is simply not made of Earth, because they are fundamentally different elements and fundamentally separate.
Now thoughts like this seem to solve the Earth/Stone problem. Because BIONICLE runs off of an elemental ontology rather than a physical ontology, and the world is fully reducible to these elements, rather than to physical matter, there just IS a difference between the ontology of a Stone and the ontology of Earth. We may not be clear on what this is, but the fact that it is a separate element ontologically means that Stone and Earth in the context of BIONICLE are not the same.
So, in conclusion, when we’re thinking about why Earth and Stone are separate elements, it seems like the answer simply is that they have a fundamentally different ontology. There is a form known as Stone, and there is a form known as Earth. These forms (as well as other elements) make up the world. This may be viewed like the dualist claim that mental and physical substance make up the world. Ultimately the Toa of Stone controls the form known as Stone, and the Toa of Earth controls the form of Earth. In addition we can say that Stone is not reducible to Earth. Instead, at their root, they are just different.
It seems to me like this, from an internal perspective, solves the ambiguity herein, and resolves the coherency of the distinction. Thoughts?