---
title: "PHI403 Lecture 12 — The Explanatory Power of Mechanisms"
type: source
tags: [philosophy-of-science, mechanism, russo-williamson, semmelweis, homeostasis]
authors: [Anjum, Rani Lill; Rocca, Elena]
year: 2023
venue: "PHI403 Causation in Science, NMBU"
kind: handout
raw_path: "raw/Philosophy of Science/PHI302 12 The Explanatory Power of  Mechanisms.pdf"
created: 2026-04-20
updated: 2026-04-20
key_claims:
  - Two scientific practices: quantitative (what and how often) vs qualitative/mechanistic (how and why).
  - Mechanisms hold more explanatory power than regularities — "married men live longer" requires a mechanism to license intervention.
  - Russo-Williamson thesis: seek both statistical and mechanistic evidence, favouring statistics in conflict (cf. Semmelweis case).
  - Causation of stability (equilibrium, homeostasis) does not fit change-based theories — counterbalancing powers produce "no change" as a genuine causal outcome.
---

# PHI403 Lecture 12 — The Explanatory Power of Mechanisms

The course's treatment of **[[concepts/mechanisms-in-science|mechanisms]]** and their relationship to statistical evidence.

Statistical vocabulary routinely smuggles causal assumptions into correlational conclusions — "increase", "prevent", "affect", "reduce", "enhance". Without a mechanism, we cannot license interventions based on a statistical finding. "Married men live longer" is statistically true but the real causal work is done by stress, diet, life-style, loneliness, depression — a marriage can affect all of these in either direction.

The **Russo-Williamson thesis**: causal claims require *both* statistical and mechanistic evidence. In conflict, favour statistics. The lecture cites the **Semmelweis case** as a cautionary tale: his hand-washing hypothesis was rejected because no mechanism of disease transmission was known, even though the statistics were striking.

**Causation of stability**: equilibrium (Moon's orbit) and homeostasis (body temperature, blood-oxygen, insulin regulation) are instances of causation where *nothing changes* — counterbalancing powers keep the system in a range. Change-based and difference-making theories struggle here; a **dynamic theory of mechanism** is needed.

The lecture reprints the EBM [[concepts/evidence-hierarchy|evidence hierarchy]] — RCT > observation > mechanism — and criticises the ranking on mechanism's behalf.

## Connections
Back-link: [[sources/2023-anjum-rocca-phi403-causation-in-science]]. Concepts: [[concepts/mechanisms-in-science]] · [[concepts/evidence-hierarchy]] · [[concepts/causation]] · [[concepts/dispositionalism]].