“Whomever smites a soul, through witnesses shall the killer be killed, and one witness shall not answer about a soul to be killed” (Bamidbar 35:30). Although the information gleaned from a straightforward reading of this verse would be that (a) witnesses are necessary for a murderer to be executed and (b) one witness is not enough to carry out an execution (and this is certainly true), the Talmud (Sanhedrin 33b-34a, see also Sifre and Yerushalmi) understands the second half of the verse to be discussing court proceedings that occur after the witnesses have already given their testimony, not the testimony itself.

Usually, after a witness has testified and the judges have started deliberating the merits of the case, students sitting before the judges can state their opinion about which decision should be reached. However, if the case involves capital punishment, since the Torah tells us to try to save the accused from being executed (35:25), only an argument for acquittal is accepted. What if the witness himself wants to present an argument about the case? Obviously, for the same reason a student is not allowed to argue for conviction, a witness can’t either. As far as whether a witness can argue for acquittal (as a student can), two opinions are expressed in the Talmud. Rabbi Yosi bar Yehudah says that a witness can argue in favor of the defendant, as the verse only says that “a witness can’t answer in a capital case to convict” (implying that he can argue for acquittal), while the Rabbanan say that a witness cannot make a case for either acquittal or conviction. Even though the verse adds the word “to be killed” (i.e. to be convicted of murder and executed), they understand this word as applying only to the students. [According to this, the verse would be read in two ways, both being true, with each excluding one of the words of the verse; “a witness shall not answer about a soul (a case of capital punishment),” with the word “to convict” being left off, and “one (of the students) shall not answer about a soul to convict,” with the word “witness” being left off.]

There are several reasons why this part of the verse is understood to be referring to what a witness says after he testifies rather than to the testimony itself. For one thing, the Torah tells us elsewhere that one witness is not enough, so this verse can’t be teaching us the same thing. This reason is put forth by the S’MaG (Negative Commandment #264) and Yad Ramah, both of whom quote D’varim 19:15. [As far as why D’varim 17:6 isn’t quoted,  Rambam (Negative Commandment #291) says this also refers to a witness not being allowed to make an argument to convict. However, according to the Rabbanan witnesses are also prohibited from making an argument to acquit, and this verse only mentions conviction. We would also need to address why preventing a witness from making an argument is taught twice (once in Bamidbar and once in D’varim) if needing more than one witness cannot be, as well as the fact that many laws are repeated in D’varim.] It should be noted that the Chizkuni and the Netziv give reasons why the Torah mentions needing more than one witness even if we already know it from another verse.

Another reason given (see Netziv’s commentary on Sanhedrin as well as his commentary on Bamidbar) is that the term usually used to signify the testimony of a witness is “ya’kum,” to establish the facts of the case, whereas here the term used here is “ya’aneh,” to respond to what has already been [attempted to be] established. [Nevertheless, the Targumim translate the word as “testify,” not “answer.”] A third reason may be the verse’s implication that two or more witnesses are needed only when it is a capital case, an implication that applies only if the verse means needing more than one witness, not if it means being prohibited from making a case for acquittal or conviction after giving testimony. [It should be noted that many, if not most, including the Rambam, say that witnesses can make an argument in civil cases, making this a valid implication, as it is only in capital cases that a witness can’t present an argument, whereas in other cases he can.]

That a witness cannot argue for or against a conviction in a capital case is listed as one of the 613 Biblical commandments. I have already referenced the S’MaG and the Rambam; the Chinuch lists it as Mitzvah #411. All three mention that this prohibition only applies to capital cases; in a monetary case, after giving his testimony a witness can make a case as to why the money should or shouldn’t transfer hands. The basis for this difference is stated quite clearly; the verse is only discussing capital cases, so can’t be automatically extended to other cases. However, the way things are explained in the Talmud raises several issues, including making such a distinction.

After telling us that Rabbi Yosi bar Yehudah only prohibits the witness from arguing for conviction because that’s all the verse mentions, the Talmud asks why the Rabbanan prohibit the witness from arguing for acquittal too. Reish Lakish says it is because doing so “gives the appearance of biased testimony.” The commentators explain that after testifying that a capital offense was committed, the witness may become nervous that his testimony will be proven false via “eidim zom’mim,” witnesses that undermine his ability to be able to testify about this case (because he was elsewhere at the time), which can have severe consequences (in this case, being put to death instead of the defendant). In order to prevent a conviction based on his testimony — which can lead to suffering the consequences instead of the defendant — the witness may therefore try to argue against a conviction. [Although from the Talmud’s wording it seems that it is the original testimony that “appears biased,” it could also be the argument that can appear specious, since it is only being made to prevent his previous testimony from leading to a conviction.] In order to avoid this “perceived bias,” we don’t let a witness argue for or against a conviction. Based on this, the Meiri (and others) ask why this concern only applies to capital cases, not to monetary cases as well, where biases can also be present.

Another issue that is raised (see Gilyon Maharsha on Sanhedrin 34a, see also Shiray Korban on Sanhedrin 4:6) is based on how the Rambam describes this law in Mishneh Torah (Hilchos Eidus 5:8). Although in Sefer HaMitzvos he mentions the reason given by Reish Lakish as to why a witness cannot make an argument against acquittal, in Mishneh Torah he says it is based on the verse itself, without mentioning Reish Lakish’s rationale, seemingly ignoring the Talmud. [Others ask how the concepts of “conviction” and “acquittal” apply to monetary cases, since ruling for one party means ruling against the other. However, if the issue is only an “appearance of bias” based on the witnesses’ earlier testimony, as far as the witness is concerned it is only arguing for or against his own testimony that is relevant, not whether there is another party equally affected by the court case.]

The consequences of the witnesses’ testimony are certainly more severe in capital cases than in monetary cases, so (as Meiri admits) we can certainly understand why there is less of an issue of “perceived bias” by the latter. Whether the issue is a possible fear of “eidim zom’mim,” or (as some suggest) of the defendant’s relatives taking revenge, or not wanting to be the cause of someone else’s death, a witness not being allowed to argue for acquittal in capital cases based on this “perceived bias” does not automatically apply to other, less severe, cases. Nevertheless, no matter how strong the concern about “perceived bias” is in capital cases, it cannot negate the Biblical mandate to try to save the defendant from execution. Therefore, Reish Lakish’s concern cannot override the implication of the verse, it must work within it.

There are two ways to understand the verse (within a “post-testimony” context). It could be saying (as Rabbi Yosi bar Yehudah has it) that a witness cannot make a case to convict in a capital case, or it could be saying (as the Rabbanan have it) that in a capital case, a witness cannot make any argument. Since the prohibition against arguing for conviction extends beyond witnesses (to students, and even to judges who had previously argued in favor of acquittal), there would seem to be no need to state such a prohibition specifically for witnesses. The upshot of the verse, then, is that witnesses are only prohibited from arguing for conviction, but they are allowed to argue for acquittal. This should also be obvious, though, since the Torah wants the accused to be acquitted. Why would the Torah need to teach us that a witness is allowed to argue for acquittal? It would seem, then, that Reish Lakesh’s “perceived bias” is needed by Rabbi Yosi bar Yehudah too, but instead of being the reason why the verse must mean that a witness cannot argue for acquittal (as the Rabbanan have it), it is the reason why we might have thought that a witness cannot argue for acquittal. (The Talmud continues by asking why, according to the Rabbanan, we wouldn’t know it was a capital case without the word “to convict,” with the answer being that the extra word teaches us that students are prohibited from arguing for conviction.)

As it turns out, then, both the Rabbanan and Rabbi Yosi bar Yehudah base their opinions on how they understand the verse, with “perceived bias” being either the reason why the verse prohibits a witness from arguing for acquittal (the Rabbanan’s perspective) or the reason why the verse must tell us that a witness can argue for acquittal. There is therefore no contradiction between the Rambam saying that the source of the prohibition against a witness arguing for acquittal is the verse and the Talmud attributing it to a “perceived bias,” as the latter is only explaining the former.

When including the prohibition in the list of Biblical commandments, where its very inclusion means it is based on a verse, there’s no reason to leave out Reish Lakesh’s reason, since it was the reason the verse was understood this way. In Mishneh Torah, on the other hand, where laws that are both Biblical and Rabbinical in origin are listed, the Rambam wanted to make it clear that the source of the prohibition is the verse, so omitted Reish Lakesh’s reason for understanding the verse that way.