In this commentary my aim has been to point out (i.) that defining levels as crucially dependent on properties has a wider and more flexible range of application than using part–whole relationships as the defining criterion; and to put forward (ii.) that levels of mechanisms and levels of emergence can be reconciled into an account of mechanistic emergence in which the property-dependent definition of levels finds application.
My argument was (a.) that descriptive pluralism, by conceiving of levels essentially as metaphors, cannot yield sufficient conceptual clarification concerning the term “level”—namely, what levels actually are and how they exist and, even undermines the goal of preserving the use of the concept in science. Further, I highlighted (b.) that in “levels of mechanisms”, as presented by Carl Craver, the core criterion for a definition of “level” is a part–whole relationship in conjunction with a constitutive relevance constraint, and that this focuses solely on the vertical dimension existing between levels, and completely omits the more important horizontal dimension of the conditions that must apply for a set of entities to be on the same level. As such, the concept is only very weakly and indirectly characterized, offering little toward its clarification and broader application. Finally, I showed (c.) that ontological novelty is not dependent on epistemic intractability, and that the ontological novelty of properties on higher levels of mechanisms is not a banal fact either in levels of mechanisms or in levels of emergence. What emergence expresses at its core is that new properties are coming into existence and that they are so strikingly novel that they might not be predictable at the moment—or seem to not be so, even in principle. They are novel to such a degree that their instantiation coinstantaneously establishes a wholly new level.
As positive proposals for an alternative view, I defined (d.) “properties” as instantiated by epistemic systems capturing specific dispositional profiles of entities, and (e.) “levels” as sets of such properties instantiated by the same or a similar epistemic system, as compared to those properties instantiated by another epistemic system. Furthermore, I (f.) provided a definition of “mechanistic emergence” implementing the core idea of emergence as aforementioned, together with the proposed definitions of “levels” and “properties”.
Concerning future directions for research, it seems most pressing to further develop the notion of an “epistemic system”. Moreover, the notion of “levels” needs to be further refined with regard to how much epistemic systems can or must differ in order for there to be a new level. Ultimately, of course, it will be intriguing to see whether the developed definitions hold in the light of practical implementations in scientific contexts.
To finish, let us come back to the initial question of whether mind and brain, or more precisely mental processes and neurobiological processes, are on the same level, which we are now in a better position to answer. So far as we acknowledge that mental properties and properties of the brain are different properties, and if we also consider how I defined levels above, we can conclude that mind and brain are in fact on different levels in this sense. But are we thus slipping back into dualism? Absolutely not, since the definition of properties developed above makes clear how it comes about that there can be different properties of one and the same thing: it is dependent on the kind of epistemic system in use to capture specific dispositions or, in short, on the epistemic context. Taking up our example of compassion once again, it is now obvious why the phenomenon did not seem to be fully captured only by reference to, for instance, physiological properties. Of course it makes sense to investigate the physiological realization of compassion, to measure autonomic parameters, conduct blood tests, or undertake fMRI scans, but it is equally important to conduct behavioural experiments or even interviews with participants to target the phenomenological experience that encompasses compassion (cf. Singer & Bolz 2013). This only means that we are doing research on all the different properties of the phenomenon of compassion. We are doing research in different disciplines with different methods, on different levels, and we are capturing different properties of one and the same thing—so let's work together to incrementally integrate those epistemic contexts and get the complete picture.
Acknowledgements
I wish to express my gratitude to two anonymous reviewers, and in particular the editors, for their extensive comments on an earlier version of this commentary, which contributed immensely to its reaching the present form.