Are the four characteristics -- production, abiding, change and destruction -- empty, conceptual constructions?

Are the four characteristics -- production, abiding, change and destruction -- empty, conceptual constructions?

Ultimately speaking, yes. I find this a difficult concept to explain so please bare with me.

Ultimately, Nirvana is the only thing that exists. Nirvana is both ever present and infinite. It is free of the four concepts of which you speak. For the sake of explanation, one could say Nirvana is the only thing that exists, and everything else we believe to exist is simply a conceptual construction or interpretation of Nirvana. Belief in those conceptual constructions is what causes the illusion of samsara to arise.

Here is a small example of how I would break this process down to explain. I know it doesn’t conform to the standard understandings of some Buddhist concepts like Nama and Rupa, but please just take this as a simplified explanation.

Imagine you see a tree. It looks as if it’s dying and will soon pass. You think how the four characteristics are present in the tree. But then you take a step back and realize that is not a tree. It is sight, which you have conceptualized to be a tree. You now think about how the four characteristics are present in sight. But then you take a step back and realize that it is not sight. It is Nirvana, which you have conceptualized to be sight. Upon observing Nirvana as the source of all conceptualization, conceptualization ends and the false self has nowhere to persist, and you become free.

Does this make production etc., perhaps even impermanence, an illusion, especially according to hua-yen Buddhism [as that's where I've seen these four characteristic enumerated]?

Yes. They are illusions, but they are helpful illusions. When studied, they can assist in guiding us towards liberation. But their usefulness comes to an end once they are observed to be illusions. This is why the Buddha says once liberation is reached, even the Dharma itself must be let go of. It no longer becomes helpful and only ties to to more conceptualization, which will pull you from the freedom you have just achieved.

Build the boat to cross the river, but don’t try to bring it with you when you reach the other side.

That being said, if you haven’t directly experienced Nirvana yet, don’t try to pretend you aren’t observing the four characteristics. It’s important not to ignore them and use them as tools to get a glimpse of the other side. Once you see Nirvana for the first time, the illusion will naturally break down, as will the understandings.

I hope this was helpful to you. I pray for nothing more than your success in your endeavors.

Well, obviously the notions of production etc are dependent on having the notion of a finite, spatially/temporaly/qualitatively bounded entity (phenomenon) that is being produced etc.

Since the bounds determining the identity of any such entity (phenomenon) are necessarily a product of an act of analysis aka imputation, its production etc. is an empty conceptual construct.

As you correctly supposed, suffering, cessation of suffering, samsara, and cessation of samsara are conceptually constructed notions in the same vein. Hence all the Mahayana talk about transcending the duality of Samsara/Nirvana, liberation from even the concept of liberation, entering true emptiness, the groundless ground etc.

The four characteristics are indeed empty conceptual constructions. It certainly makes the four, as well as impermanence and other characteristics illusion. But such is the case from the ultimate point of view. From a conventional point of view, impermanence is not a illusion, it is the very characteristic of reality. Likewise the four characteristics you mention, from the conventional point of view, they are not illusory- they are very much real- things break, things are produced and so on.

It is important to keep in mind that to be empty is to be empty of an objective existence, an independent existence. To be empty is to be dependent on other phenomenon. From the conventional point of view, all phenomenon are dependent and this is synonymous to all phenomenon being empty, from the ultimate point of view.