Reversal test

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The reversal test is a heuristic designed to spot and eliminate the status quo bias.

The reversal test[edit]

The reversal test was introduced in the context of the bioethics of human enhancement by Nick Bostrom and Toby Ord.[1] Given that humans might suffer from irrational status quo bias, how can one distinguish between valid criticisms of proposed increase in some human trait and criticisms merely motivated by resistance to change? The reversal test attempts to do this by asking whether it would be a good thing if the trait was decreased: An example given is that if someone objects that an increase in intelligence would be a bad thing due to more dangerous weapons being made etc., the objector to that position would then ask "Shouldn't we decrease intelligence then?"

"Reversal Test: When a proposal to change a certain parameter is thought to have bad overall consequences, consider a change to the same parameter in the opposite direction. If this is also thought to have bad overall consequences, then the onus is on those who reach these conclusions to explain why our position cannot be improved through changes to this parameter. If they are unable to do so, then we have reason to suspect that they suffer from status quo bias." (p. 664)

Ideally the test will help reveal whether status quo bias is an important causal factor in the initial judgement.

A similar thought experiment in regards to dampening traumatic memories was described by Adam J. Kolber, imagining whether aliens naturally resistant to traumatic memories should adopt traumatic "memory enhancement".[2] The "trip to reality" rebuttal to Nozick's experience machine thought experiment (where one's entire current life is shown to be a simulation and one is offered to return to reality) can also be seen as a form of reversal test.[3]

Double reversal test[edit]

A further elaboration on the reversal test is suggested as the double reversal test:

"Double Reversal Test: Suppose it is thought that increasing a certain parameter and decreasing it would both have bad overall consequences. Consider a scenario in which a natural factor threatens to move the parameter in one direction and ask whether it would be good to counterbalance this change by an intervention to preserve the status quo. If so, consider a later time when the naturally occurring factor is about to vanish and ask whether it would be a good idea to intervene to reverse the first intervention. If not, then there is a strong prima facie case for thinking that it would be good to make the first intervention even in the absence of the natural countervailing factor." (p. 673)

In this case the status quo bias is turned against itself, hopefully reducing its impact on the reasoning. It also handles possible arguments from evolutionary adaptation, transition costs, risk, and person-affecting morality that might otherwise complicate the simple reversal test.


Alfred Nordmann argues that the simple reversal test merely erects a straw-man argument in favour of enhancement. He also claims that both tests ignore approaches that are neither consequentialist nor deontological, plus that one cannot view humans as collections of parameters that can be optimized separately or without regard to their history.[4]

Christian Weidemann similarly argues that the double reversal test can muddy the water; weighing transition costs versus benefits might be the relevant practical ethical question in much future enhancement analysis.[5]


  1. ^ Nick Bostrom, Toby Ord (2006). "The reversal test: eliminating status quo bias in applied ethics". Ethics (University of Chicago Press) 116 (4): 656–679.
  2. ^ Kolber, Adam J., Therapeutic Forgetting: The Legal and Ethical Implications of Memory Dampening. Vanderbilt Law Review, Vol. 59, p. 1561, 2006; San Diego Legal Studies Paper No. 07-37
  3. ^ Dan Weijers, Intuitive Biases in Judgments about Thought Experiments: the Experience Machine Revisited, Philosophical Writings, No. 50 & No. 51, Summer & Autumn 2011
  4. ^ Alfred Nordmann, If and Then: A Critique of Speculative NanoEthics, Nanoethics (2007) 1:31–46
  5. ^ Christian Weidemann, Towards a Heuristic for Nanoethics: The Onus of Proof in Applied Ethics. Uncovering Status Quo and Other Biases. In Size Matters: Ethical, Legal and Social Aspects of Nanbiotechnology and Nanomedicine, Johann S. Ach, Christian Weidemann (eds.), LIT Verlag Münster 2009 (pp. 126–127)