The laws of murder appear to contain a tension of sorts with regards to killing one person in order to save another person’s life. On the one hand, there is an obligation to save the life of a potential murder victim, even if that involves killing the murderer, which is known in halakhic literature as the rule of a rodef, a pursuer. However, there is a general rule of ein dochin nefesh bifnei nefesh, we do not shed one life to save another. Thus, a woman in a difficult childbirth cannot have the baby killed once it extrudes its head, even to save her life (Mishnah Oholos 7:6). Why should the murderer’s life, therefore, be eliminated in order to save the victim? Additionally, is the concept of ein dochin nefesh mipnei nefesh identical to the reasoning that the Gemara provides for why one cannot kill someone to save himself: “who is to say that your blood is redder”?
R’ Chaim Halevi Soloveitchik in his commentary to Rambam Hilchos Rotzeach 1:9 uses the Rambam there to explain the concept of rodef. In theory, one life would never overvalue any other life (ein dochin etc.), and even an assassin would not be permitted to be killed to save his would-be victim. However, as the Rambam writes, this rule is overruled by the verse “not to pity him,” which the Rambam tells us is an independent commandment, a gezairas ha-kasuv teaching us that in this singular case, dochin nefesh mipnei nefesh. Thus, there is no contradiction between two principles, but a general principle that no life is taken for another, and a specific law overrunning this principle for a rodef.
The nature of this halakha that allows one to kill a rodef, however, remains to be seen: is this a completely independent mitzvah, or is this mitzvah an extension of the general commandment to save a Jew’s life even at the expense of violating the Torah? In other words, even though most laws are pushed aside for the sake of pikuch nefesh, saving someone’s life, this is not true regarding the prohibition of murder: one cannot commit murder to save another’s life. Once the Torah has told us that in the case of rodef, one is allowed to kill to save someone, should we assume that to be an extension of pikuach nefesh or a completely independent dispensation?
Reb Chaim suggests that the mitzvah to kill the rodef is unconnected to the rules of pikuach nefesh, because, he writes, we see from the Gemara (Sanhdrin 57b) that the permissibility (or, more correctly, obligation) to kill the rodef is equally applicable to a Ben Noach, despite the fact that a Ben Noach is not included in the more general dispensation of pikuach nefesh.
To better understand why this would be the case, it’s helpful to look at how Reb Chaim understands the concept of how pikiuach nefesh relates to the prohibition of murder in general. It is well known that murder is one of the three prohibitions that one is never allowed to violate, even if one’s life is threatened. Why does pikuach nefesh not allow someone to kill his fellow Jew to save his own life? The Gemara explains, mai chazis de-dama didach sumak tefei, dilma dama didei sumak tefei – “what makes you think that your blood is redder?” In other words, a person cannot assume that his own life is more valuable than the life of his friend. This is considered by the Gemara to be a sevara, reasoning so sound that we need no other source to tell us this halakha.
What exactly is the reasoning of mai chazis? Couldn’t the Gemara have just as easily said ein dochin nefesh mipnei nefesh? By asking rhetorically, “whose blood is redder,” the Gemara might mean that because nobody can put relative values on different people’s lives, a person must be passive and not do anything at all. This would indeed be very similar, perhaps even identical, to the concept of ein dochin nefesh mipnei nefesh – because we cannot kill one person to save another, we must do nothing at all. However, Reb Chaim (in his comments to Hilchos Yesodei haTorah Ch. 5) posits another explanation: perhaps the reasoning of mai chazis teaches us that the entire concept of pikuach nefesh is inapplicable to the prohibition of murder. Because murder itself is not merely violation a prohibition, but a violation that results in the loss of a life anyway, then the fact that a prohibition is normally pushed-off for the sake of saving someone’s life is completely irrelevant when it comes to the prohibition of murder.
This second explanation of Reb Chaim sheds further light on how Reb Chaim explains the concept of rodef. While one might have thought that the allowance to kill a would-be murderer is an extension of pikuch nefesh, once we know that the entire concept of pikuach nefesh is inapplicable to the prohibition of taking someone’s life, the Torah’s command regarding a rodef must be an independent mitzvah. Furthermore, this would explain the difference between mai chazis and ein dochin and why both concepts were needed (even if both are based upon sevara). Even if it is true that there is no applicability of pikuach nefesh when it comes to murder, one could conceivably have thought that if two people are endangering each other’s lives, then a third person would be able to arbitrarily save any one of them at the expense of the other – not by violating the sin of murder to save a life, but saving a single life, which, indirectly and unfortunately causes the loss of another. However, the concept of ein dochin nefesh mipnei nefesh teaches us that this, too, is prohibited.