As usual, thinking out loud.
I finally saw a definition of naturalism that I like. All that is, is natural, and nature is causally closed. Given my pragmatic naturalism, per Peirce and Dewey, I would add that there are more modalities of being than existence. It includes possibility and generality. I will now work out the consequences of this definition.
Causal closure does not close possibility and generality, e.g., meaning, because they are different modalities of being. Since possibility is not closed, then quality is not closed, I hypothesize. Quality as felt quality (Dewey, not Peirce) is an existential possibility, wherein chance reigns. Quality and situatedness are mutually implicated in a human situation.
What is needed is to define "cause," which surely includes efficient and material, although I am yet not well-versed enough in metaphysics to determine the relationship of emergent teleology and efficient or material causation. What is missing, prima facie, is a discussion of activity and its mode of being.
Emergent teleology requires potency, which is a triad of 1) capacity (dunamis), 2) telic activity (kinesis), and 3) realization unto actuality (entelechy). Contra Aristotle, in a Peircean framework, potentiality is equiprimordial to existence; potentiality need not inhere in actuality.
I have been trying to determine what "causally closed" practically means. I think the most concrete way to put it is that there are a limited number of natural forces, e.g., weak/strong nuclear, electromagnetic, gravitic (debatable), etc. However, that does not mean that their operation is static, e.g., since experimental cosmology indicates that the fundamental constants have changed given cosmic time. Another way to think this is, that while firstness and thirdness may not be closed, secondness qua becoming is closed. Given the rejection of eternal/timeless existence, secondness is always implicated in existence, but if causality is closed, then the possibilities of actual existence are thereby constrained. They are constrained in how something may come to be. Recall that becoming and existence are of secondness, whereas actual (determinate) existence and generality are of thirdness. Under this interpretation, the laws of nature (thirdness) specify the possibilities (firstness) and how something may come to be (secondness).
None of this adequately addresses activity as a mode of being and its relation to existence. Peirce names secondness as both activity and existence, but further study would be required to determine exactly what he proposed. For my part, if an existence is an actualized potentiality that is also an event (~concrescence) ... aha ... there it is. I should distinguish between potentiality-as-activity (kinesis) and potentiality-as-actualization. If potentiality, i.e., the whole triad, emerges through the interaction of other existences, then the difference between activity and its produced existence is clear. The produced existence of an activity is the concretion, the emergence, the realization to actuality of an activity that implicates that singular activity in a nexus of activities. This last part is key; the activity does not create its existence ex nihilo, but involves the localized nexus of activities and existences.
For a practical example, since this all becomes arcane and abstract, I constantly remind myself of the analogy of energy-matter conversion; if energy is an activity, then sometimes it becomes matter. Matter is really an emergent phenomenon of an energetic nexus that as a network gains a "body" that has extension and resistance. Likewise, early 19th century physiologists were astounded to discover that the human body converts physical contact into nervous energy--matter energy conversion--and later in that century they learned the importance of rate of change to this.
Steven Miller, astute scholar, was concerned that "nature is causally closed" leads to a "definition by reassertion of the definiendum," which was criticized by Thomas Alexander as defining "naturalism as nothing super-natural." I am sensitive to this criticism as I also find such a definition frivolous, and I hope to have addressed it. Causal closure would indeed by boring if actuality and its efficient causality were all there were to nature.
In closing, I'm not claiming to do anything new. I am just working this out for myself, for I find that I understand such thinkers as Peirce much clearer when I do so and then later discover Peirce's own argument. Feel free to comment and to give me Peirce references, especially where he must have addressed this ... somewhere....