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Introduction to Part III: Could scientific discoveries undermine, or support, ethical principles?

In Part III of this course we aim to find out whether moral psychology really is the science of good and evil. Here we start by looking at a range of claims, positive and negative, that philosophers and scientists have made about whether discoveries about moral psychology could undermine, or support, ethical principles.

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In Part III of this course we will consider whether discoveries about moral psychology could undermine, or support, ethical principles.

We will consider a variety of argument strategies in the lectures. These will draw on, and extend, the research on the psychological underpinnings of ethical abilities considered in Part I of the course.


Kant famously answered our question negatively:

‘Hier sehen wir nun die Philosophie in der Tat auf einen mißlichen Standpunkt gestellt [...] Hier soll sie ihre Lauterkeit beweisen als Selbsthalterin ihrer Gesetze [...] Alles also, was empirisch ist, ist als Zutat zum Princip der Sittlichkeit nicht allein dazu ganz untauglich, sondern der Lauterkeit der Sitten selbst höchst nachteilig [...] Wider diese Nachlässigkeit oder gar niedrige Denkungsart in Aufsuchung des Princips unter empirischen Bewegursachen und Gesetzen kann man auch nicht zu viel und zu oft Warnungen ergehen lassen, indem die menschliche Vernunft [...] gern [...] der Sittlichkeit einen aus Gliedern ganz verschiedener Abstammung zusammengeflickten Bastard unterschiebt, der allem ähnlich sieht [...], nur der Tugend nicht’ (Kant, 1870, p. AK 4:425--6).[1]

I was unable to identify an argument for this view. It may be best to start neutral and see whether there are ways in which moral psychology can inform ethics.


We will consider a variety of claims according to which discoveries in moral psychology can:

  1. inform some decisions about which intuitions to keep when considering particular cases (e.g. Kumar & Campbell, 2012);[2]
  2. show that any judgement about a particular moral scenario stands in need of justification (e.g. Sinnott-Armstrong, 2008);
  3. enhance the ability of ethicists to abstract away from personal idiosyncrasies (e.g. Rini, 2013);
  4. show that judgements about unfamiliar moral scenarios are generally unreliable (e.g. Greene, 2014);
  5. undermine the project of reflective equilibrium (e.g. Singer, 2005); or
  6. eliminate objections to systematic normative ethical theories (e.g. Singer, 2005 again).

To this end we will draw on, and extend, what we learned in Part I about humans’ ethical abilities and the processes underpinning them.

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reflective equilibrium : A method that is supposed to provide justification for claims. The idea is to gather considered judgements about particular situations and attempt to identify principles which from which those judgements could be inferred, and then to adjust the judgements and principles so that they cohere. The canonical statement is Rawls (1999) (but Rawls, 1951 is a useful earlier statement). Authoritative secondary sources are Knight (2023) and Scanlon (2002).


Greene, J. D. (2014). Beyond Point-and-Shoot Morality: Why Cognitive (Neuro)Science Matters for Ethics. Ethics, 124(4), 695–726.
Kant, I. (1870). Grundlegung zur metaphysik der sitten. Berlin: L. Heimann.
Kant, I. (2002). Groundwork for the Metaphysics of Morals. (A. W. Wood, Trans.). Yale University Press.
Knight, C. (2023). Reflective Equilibrium. In E. N. Zalta & U. Nodelman (Eds.), The Stanford Encyclopedia of Philosophy (Winter 2023). Metaphysics Research Lab, Stanford University. Retrieved from
Königs, P. (2020). Experimental ethics, intuitions, and morally irrelevant factors. Philosophical Studies, forthcoming, 1–19.
Kumar, V., & Campbell, R. (2012). On the normative significance of experimental moral psychology. Philosophical Psychology, 25(3), 311–330.
Rawls, J. (1951). Outline of a Decision Procedure for Ethics. The Philosophical Review, 60(2), 177–197.
Rawls, J. (1999). A Theory of Justice (Revised edition). Cambridge, Mass: Harvard University Press.
Rini, R. A. (2013). Making psychology normatively significant. The Journal of Ethics, 17(3), 257–274.
Rini, R. A. (2016). Debunking debunking: A regress challenge for psychological threats to moral judgment. Philosophical Studies, 173(3), 675–697.
Sandberg, J., & Juth, N. (2011). Ethics and intuitions: A reply to singer. The Journal of Ethics, 15(3), 209–226.
Scanlon, T. M. (2002). Rawls on justification. In S. Freeman (Ed.), The cambridge companion to rawls (pp. 139–167). Cambridge: Cambridge University Press.
Singer, P. (2005). Ethics and Intuitions. The Journal of Ethics, 9(3), 331–352.
Sinnott-Armstrong, W. (2008). Reply to tolhurst and shafer-landau. In W. Sinnott-Armstrong (Ed.), Moral psychology: Intuition and diversity. The cognitive science of morality (Vol. 2, pp. 97–105). Cambridge, Mass.: Cambridge University Press.


  1. ‘Here we see philosophy placed in a predicament. [...] It should prove its integrity as self-sustainer of its own laws [...] So everything empirical is, as a contribution to the principle of morality, not only entirely unfit for it, but even highly detrimental to the integrity of morals. [...] Against this careless, base way of thinking one cannot warn too often or too strongly: for human reason happily replaces morality with a bastard patched together from limbs of diverse ancestry which [...] looks nothing like virtue’ (loose translation adapted from Kant (2002, pp. 43--4)). ↩︎

  2. Compare Kumar & Campbell (2012, p. 322): ‘Empirical studies can indicate that what accounts for our divergent responses to apparently similar cases does not justify those responses, and therefore that we should withhold from drawing a moral distinction between the cases.’ ↩︎