That's not what I'm talking about. I'm talking about primal material. It's not concrete, you can't hold it. Concreteness is complex, prime material is simple. Phenomenologicaly it is vague, metaphysically it is as simple as it can possibly get.
As Plotinus said, the "One" can only be arrived at by figuring out what it isn't. And so the same thing applies to the Aristotelian Substance, for it cannot be predicated upon but merely identified as a necessary component of Being. — darthbarracuda
Now here you sound like you agree with my approach, so this becomes very confusing.
To summarise, the argument goes that we patently exist in a world of definite objects. So we start with where we are at. And then we look to what could be different in an attempt to figure out how we could come to be in such a place.
Greek metaphysics started with the idea that form was plastic and so there must be some material principle that is the underlying eternal - an ur-stuff. And as you say, something so unchanging must be ungraspable, unintelligible, as it stands beyond the descriptiveness of formed somethingness. It is like a taste so bland it can't be tasted, or a hue so pastel it can't be seen.
Anaximander gave it a name - the apeiron, or the without-limitation. But Anaximander also realised that while form (or limitation, ie constraints) was plastic, it was also based on a dialectical logic. It had to arise dichotomously as a succession of symmetry breakings.
For limits to arise in the limitless, it could only do this by the apeiron "moving apart from itself in complementary directions". And Anaximander - looking around, being empirical - not so unnaturally struck on the prime thermodynamic idea that the first parting of the apeiron would have to be into the warmer and the cooler. And then as this division proceeded to develop, it paved the way in turn for a division into the dryer and the wetter. Again, empirically, heat dries and cold dampens.
And so we have the start of a natural hierarchy of formed substances. We have the Greek elements of fire, air, water and earth as the four resulting mixtures (the hot dry and the cool dry, the hot wet and the cool wet).
Now later Greek philosophy rather messed up the simple natural purity of Anaximander's vision even as it sought to expand upon it. Obviously, the Athenians tried to work a strong notion of the divine back into it - or at least, some account of the mind seemed necessary. There was also the atomistic alternative - which did have some explanatory advantages, like stressing the notions of composition and the void. And atomism did try to argue for a rational naturalness in giving atoms the perfect shapes of the Platonic solids, or else providing them with hooks and other property-creating features.
So the notion of an ur-stuff did get confused. It became a divine spirit stuff - different from material stuff in a dualistic fashion. And it became a fundamentally particulate stuff - concrete particles rocking through an immaterial(!) void. So again a dualistic conception in that now existence was separated into the concretely material and causal contents, and an a-causal, non-material, non-involved nothingness as its cosmic container.
Thus you can see a parting of the ways from the orginally organic and holistic vision of Anaximander. Half the folk go off in a spiritual direction, thinking there is some deeper, or at least other, mind-stuff. The other half go off for the material dualism that is atomism.
But modern science has returned to a holism where existence is the transformation of simple potential via a succession of symmetry breakings, and the duality of atomism has been repaired because particles are excitations in fields and spacetime has material properties.
So we return to the question of what is the ur-stuff, the hypostatic ground, the apeiron, from which our structured existence could arise.
And as you seem to be saying, we can only characterise it in terms of it being everything our well-formed world of substantial objects is not.
So that is indeed how I would define vagueness, or the quantum roil, or the One, or whatever technical metaphysical term we might wish to give to this critical and logically necessary idea.
The things we can say about it are that it must at least be the kind of thing out of which our existence could arise. And so if our existence is about a succession of symmetry breakings, then it is some kind of perfect symmetry. And that's great, because we have some maths to get a handle on it right there.
So what is the ultimate symmetry state? I've argued the standard understanding that symmetry is about changes that can't make a change (just as symmetry breakings are semiotically the differences that do make a difference).
Absolute nothingness seems one candidate for such an ideal initial state of symmetry. But that's logically out as nothing can come from nothing.
The alternative is instead an initial state of everythingness - a complete lack of limitation on action. So some kind of dimensionless, or infinitely dimensional, chaos. Unbound fluctuation. In a state of wildness, nothing is really happening because everything is happening. And logically it is quite easy to understand how the taming of such a roil by the emergence of symmetry-breaking constraints could produce our kind of hierarchically organised world.
The classic example of such a dissipative structure is a Benard cell where global hexagonally shaped convection currents form to organise the previously chaotic thermal motions of oil molecules being heated in a pan. The many directions that the molecules are going in are reduced to the particular directions of the convection flows. The universality of a global form is imposed on the material chaos and the convection cells become a real feature of the oily world.
So we can revisit the notion of the apeiron armed with all the maths and empiricism we have gathered over the past 2300 years. If we have a clear metaphysical model of what has come out of the apeiron, we can in negative descriptive fashion now also say something scientific about the "indescribable" nature of the apeiron.
So that is why I talk about it in terms of things like unbounded fluctuation. We now understand the concrete world of substantial objects in terms of bounded fluctuations. So it is simply logical that the apeiron would be the "other" of that.
Whatever is our current best theory of fundamental being, we can reverse that out dialectically to speak about what must then be the best possible theory of the cosmic fundamental potential - the possibility that must have grounded the actuality of our Universe.