In the article “Active vs. Passive Euthanasia,” James Rachels uses a thought experiment known as the “bathtub case” to demonstrate that there is no morally relevant difference between active and passive euthanasia. According to the scenario, Smith and Jones will inherit a large sum if their respective six-year-old cousins die. Smith sneaks into the bathroom one night while the child is taking a shower and drowns him before covering up his actions. In the second case, Jones, like Smith, intends to drown the child in the bathtub. However, as he walks into the bathroom, he witnesses his cousin slip, hit his head, and fall face-down into the water and drown. Rachel claims that the only relevant difference between these two cases is that the former involves killing a child, whereas the latter involves letting a child die. Yet because Jones’s behavior seems just as heinous as Smith's, the distinction between an act of killing and one of letting-die loses its moral significance. 

With this thought experiment, Rachel hopes to show that once intentions and outcomes are taken into account, there are no morally relevant facts about killing and letting die to consider. Yet these are precisely the facts that are constitutive of the difference between active and passive euthanasia. Therefore, Rachel argues, active euthanasia is no worse than passive euthanasia, and in fact should be favored by virtue of alleviating suffering.

There are good criticisms of Rachel's argument, the most decisive of which rests on the possible difference between the moral status of Smith, who intentionally kills his cousin; and Jones, who merely intends to do so. Jones comes close to carrying out his plan, yet we cannot be sure if he would have actually done so. Consider, for example, the kind of acts we all admire. It is not uncommon for a person to consume heroic narratives, admire brave characters, and even daydream about personal feats of valor. One could be obsessed with the idea of courage, yet until that moment comes when the split-second decision must be made, whether one can find the courage or not remains a mystery. That is why we admire people who perform acts of courage and not those who merely intend to do so (should the opportunity arise). For even the most sincere intentions cannot reveal one’s true character. In the same way, Smith has actually done the murder that Jones merely intends. There is no doubt about the moral status of Smith’s character, whereas the extent of Jones’s depravity remains elusive. And although Jones’s possible failure does not make him much less guilty than Smith, the unknowable difference between them is a morally relevant one. Perhaps Jones’s character is not completely corrupt and some part of his psyche would rebel against his plans at the crucial instant.

On the whole, Rachel’s thought experiment seems to close some of the presumptive moral gap between active and passive euthanasia; however, it falls short of its ambitious attempt to draw their moral equivalence.