The Trolley at the Reservoir
A dam inspector named Priya has 40 minutes before a scheduled controlled release. She discovers that the release gate is jammed and will open fully, flooding a lower valley where 12 workers are repairing a levee. She cannot reach them in time by road. However, she can divert the water into a disused quarry channel; doing so will drown a lone surveyor, Tom, who is taking measurements in the channel and is unaware of the risk. Priya has no way to warn Tom: his radio is off and he is 900 metres away behind a ridge. Activating the diversion takes 15 minutes and has a 10% chance of failing entirely, in which case all 12 workers drown and Tom survives. If she does nothing, the 12 drown with near certainty.
1. Using act-utilitarian reasoning, what should Priya do? Show the calculation and identify two empirical uncertainties that could change the verdict.
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An act-utilitarian compares expected total welfare of each option.
Do nothing: 12 deaths with near certainty. Assign disutility −12 (plus collapse of levee, economic harm, trauma to families).
Divert: 10% chance of failure → 0.10 × (−12) + 0.90 × (−1) = −1.2 − 0.9 = −2.1 expected deaths. Plus the 15 minutes of delay risk and possible damage to the quarry channel.
On expected-value grounds, diversion is clearly preferable: −2.1 versus roughly −12.
Two uncertainties that matter:
- The 10% failure estimate. If the true failure probability is above about 0.92, the expected deaths from diverting exceed 12 and the verdict flips. Priya should ask how the estimate was derived.
- The status of the surveyor. If Tom is a trespasser who ignored signage, some utilitarians might discount his welfare slightly; if he is a contractor sent there by Priya's own employer, the institution bears extra responsibility. Either way, the numbers dominate unless the probability estimate is badly wrong.
A sophisticated answer notes that rule-utilitarian considerations (public trust in dam authorities, the precedent of sacrificing individuals) may push toward seeking consent or a third option, but on the stated facts act-utilitarianism favours diversion.
2. A Kantian critic objects that Priya would be using Tom merely as a means. Reconstruct this objection and assess whether it succeeds.
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The Kantian objection runs: Priya proposes to kill Tom in order to save others. Tom has not consented, cannot be warned, and is being treated as a tool for the safety of the 12. The formula of humanity forbids treating persons merely as means; Tom's death is the instrument by which the 12 are saved, so the act is impermissible regardless of the arithmetic.
Assessment: the objection has force but is not decisive as stated. Three replies are worth developing.
- 'Merely' is doing work. Kant does not forbid all foreseen harm to persons; he forbids using them merely as means. A driver who swerves to avoid a child and hits a pedestrian does not thereby use the pedestrian. Priya is not coercing Tom or deceiving him; she is redirecting a threat that already exists. Whether this is 'using' him or 'allowing harm to fall on him' is exactly the contested point.
- The maxim test. Priya's maxim might be: 'When a flood threatens many and one person can be sacrificed without consent, do so.' Universalised, this licenses authorities to kill uninformed individuals whenever numbers favour it - a world in which no one can trust that they will not be quietly expended. That looks like a contradiction in will for anyone who values security.
- Institutional duty. A Kantian may argue Priya's real duty is to her role: she should not personally authorise a killing but should escalate, record the decision and demand a procedure. This preserves respect for persons without pretending the 12 can be ignored.
A strong answer concludes that the Kantian objection identifies a genuine moral cost - Tom is wronged even if the act is justified - and that this cost should shape how the decision is made, not merely whether it is.