What is the form of causation in health and disease, and intervention?

By David Evans

In a paper with a very long title, recently published in Medicine Health Care and Philosophy, Roger Kerry, Nic Lucas and I set out some ideas about how causation applies to relationships between health and disease. In particular, we focused on how treatment (intervention) might act to limit disease and restore health.

Here’s a summary of the main points:

  1. The pathological model has been the dominant view of disease. It consists of three chronological stages: aetiology, pathology, patho-physiology.
  2. Interventions can be applied to any of these stages, depending upon the disease.
  3. Engel (1977, 1980) extended the pathological model to include psychological and social constructs, although pathology can only exist within a person.
  4. We adopt a dispositional view of causation (see Mumford & Anjum 2011 for lots more on this).
  5. Dispositionalism holds that objects are the relata of causative transactions.
  6. Objects manifest their dispositions. We call these ‘actions’ when they act upon other objects.
  7. Actions involve transfers of energy, which is a conserved quantity.
  8. Mechanistic chains can be constructed using alternating objects and actions.
  9. The full breadth of the biopsychosocial model suggests that psychological and social constructs can be objects. This is the biggest conjecture in the paper.
  10. This means that psychological constructs (e.g. cognitions) and societal constructs (e.g. nations) can be considered objects with dispositions – this is what we term ‘biopsychosocial dispositionalism’. This is the big consequence of the above conjecture.
  11. Psychological and social/societal objects have causal powers (dispositions) and can act upon other objects. These actions still involve energy transfers.
  12. We predict that all psychological constructs will be either an object or an action. This is the second biggest conjecture in the paper.
  13. As a consequence of the above, interactions in health, disease and intervention utilise object-action mechanistic chains.
  14. Using a fully biopsychosocial view of objects, interventions can act upon a disease pathway in any of three possible ways: they can ‘share’ an object in a disease/harmful mechanistic chain (simultaneous action), or can add and/or remove objects in a disease/harmful mechanistic chain.

Understandably, some initial feedback to the paper related to how we can stretch the term ‘objects’ to apply to psychological or societal constructs. The latter is easier to argue. Any object consists of other objects. Solid objects consist of molecules, which consist of atoms; atoms consist of protons, neutrons and electrons; these consist of smaller particles, and so on. If we use biological objects (since we are focusing on health), we can scale upwards from molecules to cells, organisms (e.g. a whole person), and then we get to social/societal ‘objects’: couples, families, communities, cultures, nations and finally the biosphere.

This hierarchical idea is not new. Engel (1980) described these as natural ‘systems’, but little stretch of the imagination is required to see any of these as objects. Do these societal objects have dispositions? To me, the answer must overwhelmingly be ‘yes’, and on so many levels. As one looks up and down Engel’s scale, a new set of dispositions emerge for each object; something of a test for a different class of object, I suspect. This is another demonstration of the importance of emergence in causation. Interestingly, nations are largely defined by laws, but I would argue that a law be considered a societal object too; they certainly have dispositional characteristics and real world consequences.


Figure 1. Engel’s hierarchy of natural systems.

Can psychological constructs reasonably be considered objects with dispositions or causal powers? I would again argue that they can. Again, psychological processes can certainly lead to real-world changes; this relates to the important topics of consciousness and free-will. We argued that causative transactions in physical mechanistic chains will either be an object or an action, and we are not the only ones to think in such dualist terms. Scholars considering mechanisms have previously described transactions as consisting of just two types of component: these have been described as entities and activities (Machamer et al 2000), and parts and operations (Bechtel & Abrahamsen 2005). One of our big predictions is that psychological constructs will continue this dualism, being either objects or actions. As I stated above, actions should involve energy transfers, and “energy transfers certainly occur within the CNS during a variety of psychological processes; ample evidence has linked specific CNS regions to particular psychological processes, having been gained through the use of modern neuroimaging techniques, such as functional magnetic resonance imaging (Bechtel 2008), and neurophysiological measures, such as event-related potentials (Woodman 2010).”

Finally, getting back to health, disease and interventions. If you are happy to accept the above, the mode of interaction between interventions and disease pathways can be reduced down to three possibilities: interventions may either act through objects being shared between converging mechanistic chains, or through the removal and/or insertion of objects in such chains. Have a look at the table below for some specific examples.

Examples of forms common to both harmful processes and appropriate interventions (based on Evans et al 2016).



Target process Common form Intervention via Outcome
Parachute Person falling from high altitude Mass of person Shared object Reduced velocity
General anaesthetic Consciousness Central nervous system Shared object Reduced pain experience
Graded exposure to trigger Phobia Cognition Shared object Reduced sensitivity to trigger
Massage Pain Somatosensory nervous system Shared object Reduced pain (analgesia)
Resistance training Muscle weakness Muscle Shared object Increased muscle strength
Insulin injection Diabetes mellitus (type 1) Insulin Inserted object Reduced blood glucose
Endovascular stent insertion Arterial aneurysm Arterial wall Inserted object Prevention of arterial rupture
Stem cell insertion Damaged tissue Cells Inserted object Functioning tissue
Organ transplant Damaged organ Damaged organ Inserted object Functioning organ
Sunscreen application Sunburn Ultraviolet light Inserted object Reduced skin damage
Surgical resection Cancer Malignant cells Removed object Removed pathology
Antibiotics Bacterial infection Bacteria Removed object Removed infection


Bechtel W. 2008. Mental mechanisms: Philosophical perspectives on cognitive neuroscience. London: Routledge.

Bechtel W, Abrahamsen A. 2005. Explanation: a mechanist alternative. Stud Hist Philos Biol Biomed Sci. 36(2):421-41.

Engel GL. 1977. The need for a new medical model: a challenge for biomedicine. Science 196:129-36.

Engel GL. 1980. The clinical application of the biopsychosocial model. American Journal of Psychiatry 137: 535-44.

Evans DW, Lucas N, Kerry R. 2017 The form of causation in health, disease and intervention: biopsychosocial dispositionalism, conserved quantity transfers and dualist mechanistic chains. Med Health Care and Philos (2017). doi:10.1007/s11019-017-9753-6

Evans DW, Lucas N, Kerry R. 2016. Time, space and form: Necessary for causation in health, disease and intervention? Med Health Care Philos 19(2):207-13.

Machamer PK, Darden L, Craver CF. 2000. Thinking about mechanisms. Philosophy of Science 67(1):1-25.

Mumford S, Anjum RL. 2011. Getting Causes from Powers. Oxford: Oxford University Press.

Woodman GF. 2010. A brief introduction to the use of event-related potentials in studies of perception and attention. Atten Percept Psychophys 72(8):2031-46.


One comment

  1. Just a quick thanks for your work. Such an important but often underplayed aspect of critical thinking, especially necessary in an increasingly complexified healthcare system.


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