For Nagarjuna, the doctrine of the emptiness of formative causation is the adequate middle way between two extremes. What does that mean?
The idea of the middle way is the ideal promoted by Buddhist sages. This is an application of the idea that there is a middle way between the two extremes of being a slave to one’s desires and asceticism.
With respect to formative causation, Nagarjuna thinks that the doctrine of dependent origination from conditions, which is the same as the doctrine of the emptiness of formative causation, is the adequate middle way between two extremes.
Like Hume in western thought, Nargarjuna believes that our conventional thinking and discourse accurately reflect the brute inexplicability and regular coherence of the world.
The extreme of reificationism makes the mistake of thinking that our ordinary conventional discourse denotes genuine causal powers between causes and effects. Since no such causes are experienced, they are unintelligible.
The extreme of nihilism makes the mistake of thinking that there is no possibility of appealing to experienced phenomena at all in order to explain what happens. In fact, regularities between and among event types occur frequently.
All phenomena arise from conditions. Those phenomena, however, lack essences. Since, like the Buddha and Hume, Nagarjuna is a nonsubstance ontologist, conditions don’t give rise to phenomena with essences. If not from conditions, where else could [fixed, eternal, independent] essences come from?
Unless objects had substantial individual essences [substrata, “undesignated matter”], how could there be absolute others by means of which to identify phenomena? If phenomena cannot be absolutely singled out apart from others, how could they be independently characterized? Objects that lack an intrinsic nature cannot be essentially different. Objects that are not essentially different, are interdependent, which is point of the doctrine of dependent co-origination; in other words, formative causation is empty.
What, then, holds the world together? Since causation is empty, it’s nothing but the regularity of conditioned dependent arising. Sometimes the regularity obtains and we understand what’s going on, and sometimes it doesn’t and we realize that we don’t understand what’s going on. Therefore, our explanations depend upon regularities, and, in our theories, we explain regularities by referring to additional regularities. That’s all.
Nagarjuna has a commonsense, as opposed to metaphysical, view of the world.
If this topic interests you, I strongly recommend Jay L. Garfield’s translation of and commentary on Nagarjuna’s Mulamadhyamakakarika.