Podcast Summary

Episode Overview

Podcast: New Books Network – New Books in Philosophy
Host: Carrie Figdor
Guest: Kenneth Aizawa, Professor of Philosophy, Rutgers University-Newark
Book Discussed: Compositional Abduction and Scientific Interpretation: A Granular Approach (Cambridge University Press, 2025)
Date: January 10, 2026

This episode delves into Kenneth Aizawa's new book, where he proposes a novel account—singular compositional abduction—of how scientists infer the existence and structure of unobservable entities from experimental data. Focusing on detailed historical case studies such as Hodgkin and Huxley’s work on action potentials and Watson and Crick's discovery of the DNA double helix, Aizawa critiques dominant philosophical accounts of scientific reasoning, especially prevailing views on abduction and mechanistic explanation.

Key Discussion Points and Insights

Origins and Motivation for the Book

• Aizawa's Background: Progressed from literature to philosophy, focusing on philosophy of psychology and topics like connectionism, extended cognition, and multiple realization. (03:31)
• Catalyst for the Book: Discontent with existing philosophical models—especially the “mutual manipulability” criterion in new mechanist philosophy and the lack of fit with actual scientific practice. Decided to revisit historic scientific cases to develop a more empirically grounded account of scientific reasoning. (03:31–06:25)

Defining Compositional Abduction

• Parade Example – Hodgkin & Huxley:
  • Scientists sought to explain a particular current observed in the squid axon by postulating that sodium ions (unseen, unmeasured at the time) entering the axon were responsible for the event. (08:56–10:20)
  • Compositional explanations work by explaining phenomena (such as a current in an axon) in terms of the properties and activities of underlying components (ions, membrane permeability changes). (10:56–12:20)
• Other Canonical Cases:
  • Van’t Hoff's postulation of tetrahedral carbon structures to explain optical activity observed in chemical compounds.
  • Watson and Crick's inference of DNA’s double helix structure from X-ray photographs. (12:51–15:01)

“That’s probably the most famous compositional abduction in all of science. No one’s, I think, theorized it that way, but that’s, I think what was going on.”
— Kenneth Aizawa, (14:30)

Intra-level vs. Inter-level Experiments

• Intra-level: Manipulate and measure properties at the same organizational level (e.g., within one axon).
• Inter-level (per New Mechanists): Manipulate and measure phenomena across different organizational levels, e.g., manipulating a system and measuring effects in its parts.
• Aizawa's Argument: Actual scientific reasoning often involves intra-level experiments, with lower-level entities postulated to explain observed data—not always directly manipulated/measured as new mechanist accounts assume. (15:21–17:01)

What is Compositional Abduction in Reasoning?

• Abduction Defined:
  • Abduction is the process of explaining an observed fact (explanandum) by postulating an underlying phenomenon or entity (explanans).
  • For Aizawa, abduction also serves to confirm the existence of the postulated entity or explanation, contrary to the dominant view. (19:13–20:31)
• Contrast with Peirce & IBE:
  • Peirce: Abduction introduces hypotheses but does not confirm them; confirmation requires further testing (hypothetico-deductive method).
  • Standard IBE (Inference to the Best Explanation): Abduction is equated with selecting the best hypothesis among competitors.
  • Aizawa's View: Abduction provides confirmatory evidence for what is hypothesized—each abduction adds evidence by mustering background information and linking it to specific experimental outcomes. (21:07–24:47)

“Abduction works, I say, by confirming the explanans. That’s the idea. The explaining thing is given a reason to, to, to be something you take seriously. The explanans has been to some degree confirmed.”
— Kenneth Aizawa, (19:57)

Abduction is Not Equivalent to IBE

• Critique of the Dominant Package: IBE involves both explaining data and comparing rival hypotheses through criteria like simplicity, breadth, etc.
• Aizawa's Narrower Focus: He analyzes the reasoning that happens in individual experiments, not theory choice across a corpus. In these single cases, emphasis is on linking a specific observation to a possible explanation, not on eliminating rivals. (29:26–33:07)

“IBE is a bigger package. It tries to cope with two issues... Abduction, as I understand it, doesn’t address that [choosing between rivals].”
— Kenneth Aizawa, (30:33)

On Generalization and Scientific Reasoning

• Generalization: Aizawa explicitly brackets questions about how scientists generalize findings from one experiment or sample to broader contexts (e.g., from one squid axon to all neurons or to humans). His account focuses tightly on the inferential step within one experimental context. (36:16–39:51)

Normativity: Should Philosophers and Scientists Care?

• Descriptive, Not Prescriptive:
  • Aizawa insists his account captures what scientists actually do, not what they ought to do. (41:07–44:00)
  • However, the cases he studies are ones lionized by scientists (e.g., Nobel-winning work).
• Normative Implications:
  • If philosophers misdescribe actual practice, their prescriptive recommendations lose relevance.
  • Scientists, especially in psychology, should reflect on the role of abduction in scientific progress—behaviorists like Skinner rejected abduction, while others (e.g., Chomsky) embraced it to argue for innate structures. (45:12–46:23)

“Abduction is how you get at the unobservable world. It’s how you get at the deep past. It’s how you get at microscopic entities. You can’t see them, right? ... Many working on mental representations have dragged their feet on embracing abduction.”
— Kenneth Aizawa, (46:36–47:30)

Critique of New Mechanists and Mutual Manipulability

• Mechanist Approach: New mechanists appeal to “mutual manipulability”—the idea that you manipulate an upper-level phenomenon and observe effects at the lower level, and vice versa.
• Aizawa's Objection: Many scientific explanations do not involve direct manipulation or measurement of postulated components (e.g., individual ions in axons); these are inferred, not directly observed or controlled. (50:40–53:19)

“That is what set me off six years ago, that picture that You can't. You cannot manipulate an individual ion. You can't measure an individual ion. You just can only postulate them.”
— Kenneth Aizawa, (51:32)

Looking Ahead

• Aizawa’s Next Steps: Plans to develop a bigger account situating abduction within the rationalist/empiricist divide, and to carry this analysis into philosophy of psychology, especially mental (and neural) representation. (54:50–57:24)
• Abduction’s Hidden Complexity: Suggests that postulating entities for explanation and then searching for empirical confirmation are distinct inferential steps that deserve separate analysis.

Notable Quotes and Memorable Moments

• On the book’s approach:
  “The book is a science-first approach. It’s not like, it seems to me, at least at the time, a methodologically groundbreaking approach. But it does now seem to me that it’s just not the way new mechanists have done it.” (06:25)

• On resistance to alternative views on abduction:
  “When I say abduction is not IBE, they, they just, it just makes reviewers angry... It’s just not a position they are, they seem prepared to entertain. It’s a... you are just out of your mind.” (21:13)

• On the practical scientific impact:
  “Psychology would not exist essentially without abduction. And B.F. Skinner rejected abduction... The central, pivotal part of 20th-century psychology. To me, it’s just huge.” (45:41)

• Summing up the methodological difference:
  “For me, it was just brutally hard work. But he’s not, he’s not going at it that way.” (52:37)

Important Timestamps

• 03:31 | Aizawa’s intellectual journey and motivation for the book
• 08:56–12:20 | Key example of compositional abduction: Hodgkin and Huxley’s solution to the action potential
• 12:51–15:01 | Broader scientific examples (DNA structure, carbon stereochemistry)
• 15:21–17:01 | Distinction between intra-level and inter-level experiments
• 19:13–20:31 | What is compositional abduction and how does it function in reasoning?
• 21:07–24:47 | Contrasting Aizawa’s view with Peirce and IBE
• 29:26–33:07 | Why abduction is not (just) inference to the best explanation (IBE)
• 36:16–39:51 | Why generalization is outside the scope, and limitations of the account
• 41:07–44:00 | Descriptive vs normative aims: relevance for philosophers and scientists
• 45:12–46:23 | Abduction in the history and philosophy of psychology
• 50:40–53:19 | Main critique of mechanistic and mutual manipulability approaches
• 54:50–57:24 | Future research agenda: philosophy of mind and abduction

Final Thoughts

Kenneth Aizawa’s “Compositional Abduction and Scientific Interpretation” offers a tightly-focused, empirically-grounded analysis of how scientists actually infer unobservables, mounting a challenge to received wisdom in philosophy of science. Through meticulous historical cases and a “granular” focus, Aizawa both carves out an overlooked form of scientific reasoning and calls philosophers to greater attention to the actual practice of science.