The problem with this is that there are a great variety of different Buddhisms which, correspondingly, have different ways of articulating these matters.
For example, Pali Buddhism (which roughly corresponds with Theravada Buddhism) has a view which corresponds with the Mahayana two truth view, where ultimate reality refers to the nature of conventional reality, when conventional reality is perceived through the lens of the 4 noble truths, the 3 characteristics (impermanence, suffering, and non-self), and its own understanding of dependent origination, etc.
In Nikaya Buddhism (early textual Buddhism, which includes Pali Buddhism), the contrast between samsara (the cycle of birth and death) and nirvana can also be seen as reflecting an understanding akin to the two truths; where samsara represents the conventional realm of conditioned existence, and nirvana represents the ultimate goal, free from suffering and the cycle of rebirth.
The Udana scripture speaks of an unborn reality, which is distinct from the born, the transient phenomenal world, which is a kind of two truths doctrine (although it wasn’t called this by early Buddhists).
Then in Mahayana there is a whole variety of different ways of conceptualising the world.
Yogacara Buddhism talked about the 3 natures: the fabricated (or constructed), the other-dependent, and the perfect.
Madhyamaka Buddhism talked about the emptiness of phenomena, but even here this emptiness can be understood in different ways, which is why there are different schools (in Tibet, for example) which reflect these differences of approach.
The influence of Tathagatagarbha literature is also responsible for a different way of understanding the two truths doctrine. The teachings of Tibetan scholars like Longchenpa and Dolpopa (especially Dolpopa) permit a view of emptiness which is similar to the one you outlined above: a purely negative emptiness of phenomena (along the lines set out by Nagarjuna and Madhyamaka philosophers), and a positive emptiness of the kind referred to in Tathagatagarbha literature. In Tibet this difference is known as rangtong and shentong emptiness.
This distinction also exists in East Asian Buddhism, which was also influenced by Tathagatagarbha literature. East Asian Buddhism is generally a mixture of Yogacara, Madhyamaka and Tathagatagarbha views (as well as esoteric views), which helps to explain the diversity of explanations that exist in Tiantai and Huayan Buddhism, for example.
Hindu philosophers like Gaudapada and Shankara were also influenced by Mahayana Buddhism, which may help to explain how they created their own versions of the two truths doctrine: conventional reality, and absolute reality (i.e. Brahman). Or a triple layer view if one makes a distinction between absolute reality with qualities and without qualities. Or a quadruple layer reality if one adds the role played by thought in creating illusion (maya): nirguna paramartha, saguna paramartha, conventional reality (vyavahara), and the illusions created by “maya”.
So, as one can see, the way one divides up the world depends on one’s underlying assumptions, one’s philosophical framework for understanding, the texts one is conforming to, as well as one’s understanding of those texts and the philosophical framework.
As I have said already, for me the simplest way of approaching all this is in terms of
- the world we perceive through our senses, which refers to the way the world exists in the actual, common sense way that it does
- the world we create through our thoughts and concepts, through our imagination and thinking
- and the absolute truth of the world, the universe, in its ground (if such a thing can be realised).
But to approach this from the level of theory will always have its limits, it will always be limited to theory. Which is why the two truths doctrine is problematic. It already assumes an understanding of the absolute view which may just be an assumption in thought. Nagarjuna’s emptiness of a dependently originated world is a logical emptiness. It is emptiness at the level of reductio ad absurdam. He may have had his own insight into truth, but his arguments do not depend on insight but logic. And so his two truths are assumptions in logic, in thought. Similarly with all these other ways of splicing up the works.
The difference with what Krishnamurti proposed is that thought is the very reality that is being questioned. The universe may be empty, emptiness may be energy, etc - but thought is always limited, and so only a mind that is empty of thought can possibly realise a deeper truth (if such a truth exists). Science can explore the nature of matter and energy up to a point (through quantum mechanics, black holes, etc), but science is always provisional, theoretical, limited by the limits of our thinking and conceiving.
Can the mind ever go beyond thinking and conceiving? This is the question for me.