Monday, September 9, 2019

Eleven varieties of contrastive explanation

In connection with free will, quantum mechanics or divine creation it is useful to talk about contrastive explanation. But there is no single generally accepted concept of contrastive explanation, and what one says about these topics varies depending on the chosen concept.

To that end, here is a collection of definitions of contrastive explanation. They all have this form:

  • r contrastively explains why p rather than q if and only if r explains why (p and not q) and [insert any additional conditions].

They vary depending on the additional conditions to be inserted. Here are some options for these:

  1. No additional conditions.

  2. r makes p more likely than q.

  3. r cannot explain q.

  4. r wouldn’t explain q if q were true instead of p.

  5. r wouldn’t explain q as well as it now explains p if q were true instead of p.

  6. q wouldn’t be explained by r or by any proposition with r’s actual grounds if q were true instead of p.

  7. q wouldn’t be explained by r or by any proposition with r’s actual grounds as well as r now explains p if q were true instead of p.

  8. the conjunction of everything explanatorily prior to p makes p more likely than q.

  9. r entails (p and not q).

  10. r entails the truth of p.

  11. r entails the falsity of q.

It is not possible to normally have contrastive explanations of indeterministic free choices or quantum events in senses 9–11, and probably sense 8, but it is possible (with an appropriately metaphysical theory of free choice or quantum events) in senses 1-7. As for the case of contingent divine creative decision, things depend on divine simplicity. Without divine simplicity, contrastive explanations are possible in senses 1–7. Interestingly, if divine simplicity is true, then it is not possible to have contrastive explanations of contingent divine creative decisions in senses 6 or 7.

In what I said above, I assumed that the explanandum cannot be a part of the explanans. If following Peter Railton one drops this condition, then contrastive explanation of all three phenomena (with or without divine simplicity) becomes possible in all the senses.

Lesson: When one talks about contrastive explanation, one needs to define one’s terms.

Acknowledgments: I am grateful to Christopher Tomaszewski for in-depth discussion that led me to recognize the important difference between 4–5 and 6–7. And the Railton point is basically due to a remark by Yunus Prasetya.


Alexander R Pruss said...

I've edited the post to include what is now numbered 8. I think other versions of the tool in 8 -- the use of the conjunction of all facts explanatorily prior to p -- may be useful as well.

Walter Van den Acker said...


How can, given divine simplicity, the explanandum be a part of the explanans?
Say, the explananadum is the existence of this world. Then, the existence of this world is a part of the explanans, which is God('s will). But per Divine Simplicty, God has no parts.

Alexander R Pruss said...

Technically, the explanans and explanandum are propositions, not entities like God or a will. The theistic version of the Railton proposal would be that the proposition that w1 is actual is explained by the proposition that God had the power to actuate world w1 and w1 was actually actuated. The "and w1 was actually actuated" is what (basically) contains the explanandum.

Walter Van den Acker said...


But "God had the power to actuate w1" is a part of "God had the power to actuate w1, w2, ..."