False Alarm, Part II: Does Halacha Accept the Polygraph?

Adapted from the writings of Dayan Yitzhak Grossman

April 30, 2026

Our previous article cited the psak of two distinguished poskim, the Eimek Halacha (R’ Yehoshua Baumol) and the Debrecener Rav (R’ Moshe Stern), that if a polygraph indicates that witnesses are lying, their testimony is rejected. But two other prominent poskim, the Tzitz Eliezer (R’ Eliezer Yehudah Waldenberg) and R’ Ovadia Yosef, reject the idea that polygraph results have any evidentiary weight. In two divorce cases from the years 5743-44/1983-84 (in one of which Rav Waldenberg and Rav Yosef sat together on the bais din), the husbands suspected their wives of infidelity and requested that they be subjected to polygraph examinations. In a pair of very similar appellate rulings, they each concluded that the device lacks halachic significance.[1]

In his rulings, Rav Waldenberg initially raises the technical problem of the polygraph’s unreliability:

In my opinion, there is no place at all for this in halacha, both because the machine has no ability to prove anything with certainty and because many problems commonly arise, for various reasons, as even secular court judges admit.

This argument would seem to leave open the possibility of accepting lie detection if the technology improved and became established as reliable. But he adds fundamental objections to the use of polygraphs in bais din, which may extend to any such device:

And Chazal already established for us in Psachim 54b that one of the seven things that are concealed from human beings is that a person does not know what is in his friend’s heart.

But the primary reason to reject it…is that it is a decree of the Torah (gzeiras haTorah) that only by the word of two witnesses shall a matter be confirmed.[2]

In support of this principle, he cites a Gemara (and a similar passage in the Targum on Kohelless):

But if Kohelless was indeed as knowledgeable as Moshe, how do I uphold the pasuk, “Kohelles sought to find words of delight” (Kohelless 12:10, which implies that he sought to be as knowledgeable as Moshe but was denied)? The answer is that Kohelless sought to adjudicate using the wisdom of the heart, without witnesses and without defendants having received a warning. A Heavenly voice came forth and said to him, “‘And words of truth are recorded properly’ (the rest of the above pasuk). And it says in the Torah, ‘By the word of two witnesses…’”[3]

Rav Waldenberg argues:

It is beyond all doubt that the wisdom of Shlomo to discern what is in the hearts of men and whether the words in their mouths are true was certainly many, many times greater than what the polygraph can demonstrate. Nevertheless, he was prevented by Heaven from judging based on this, but rather, “and words of truth are recorded properly” and “by the word of two witnesses.” So a fortiori there is no place according to halacha to be aided in psak by polygraph results, and there is no basis to obligate someone to be examined by such a machine.[4]

It is unclear whether this argument leaves any room for relying on lie detection technology. If there really is a gzeiras haTorah establishing witness testimony as the sole source of truth in judicial proceedings, that would seem to categorically exclude it. But the existence of such an absolute gzeiras haTorah is flatly contradicted by the Rambam (and Shulchan Aruch):

A judge may adjudicate monetary cases based on factors that he is inclined to regard as true and that he feels strongly in his heart are so, even though there is no clear proof. Needless to say, if he knows something with certainty, he should judge according to his knowledge…

All such matters are given over solely to the heart of the judge to decide, according to what he sees to be the true judgment. For what, then, did the Torah require two witnesses? When two witnesses come before the judge, he must judge according to their testimony even if he doesn’t know whether they testified truthfully or falsely.[5]

All this is the basic law. But when improper courts proliferated—and even if they were proper in their deeds, they weren’t sufficiently wise and imbued with understanding—most Jewish courts agreed that…and that a dayan should not adjudicate based on the reliance of his mind rather than on knowledge, in order that every layman not say, “My heart believes this person’s words and my mind relies on that.”[6]

Rav Yosef also rejects the polygraph, for both factual and halachic reasons. He adduces numerous sources for the principle that we do not rely on an umdena, even an umdena demuchach, to compel a defendant in a civil case to pay a plaintiff. (But puzzlingly, he does not acknowledge the aforementioned Rambam and Shulchan Aruch.) He adds that although we may rely on an umdena to allow a defendant not to pay a plaintiff, in his opinion that would not apply to a polygraph. The reason is that the device is “an inferior umdena (umdena gruah), because sometimes there are particular reasons for the subject’s hisragshus (excitement) and elevated blood pressure, and there are no compelling grounds whatever to establish that he is lying.” Like Rav Waldenberg, Rav Yosef further adduces Chazal’s account of the Heavenly rejection of Shlomo Hamelech’s desire to judge without witnesses and without warnings as an argument against the lie detector.

Rav Yosef cites and rejects Rav Baumol’s favorable view: “In my humble opinion, he has gone too far in placing so much trust in the polygraph in opposition to the testimony of valid witnesses…” But he concludes by explicitly leaving the door open to more reliable technology:

Perhaps if, in the course of time, scientists will improve the machine to be more truthful and accurate, we might adjudicate per its results, but currently it does not seem reasonable to me to rely on it…

R’ Yitzchak Tzvi Ushinsky, a dayan in Yerushalayim, also argues that for a variety of reasons, a dayan may not rely on polygraphs even if he personally trusts them, because of the above Rambam about the agreement of most batei din.[7] It may be countered, however, that that agreement may have been limited to judging based on personal intuition—”factors that he is inclined to regard as true and that he feels strongly in his heart are so”—and might not extend to standardized techniques.

Rav Ushinsky proceeds to cite a number of authorities that maintain that even today we may rely upon what the dayan sees as an umdena demuchach. But he argues that “it is implausible to classify the polygraph as an umdena demuchach, particularly due to the fact that its results have not been accepted in other courts either.” This leaves the door open for new lie detection methods, should they be demonstrated to be reliable and become well accepted.

[1]Shu”t Tzitz Eliezer cheilek 16 siman 47 os 10 and cheilek 20 siman 57 os 2 (the two rulings are quite similar, with the latter apparently constituting an expansion of the former); Shu”t Yabia Omer cheilek 7 C.M. siman 8 from os 2.

[2]See Dvarim 19:15.

[3]Rosh Hashanah 21b.

[4]Tzitz Eliezer cheilek 16 ibid.

[5]The Radvaz comments: “We can learn from here that if the dayan knows the witnesses testified falsely, he should not say, ‘A chain (i.e., responsibility for the miscarriage of justice) will hang around the necks of the witnesses.’ Rather, he should judge based on what he knows and not be concerned about the witnesses.” The Radvaz is clearly referring to the rule of din merumeh (see our previous article), the source of that expression. But the Gemara derives the rule from the pasuk “Distance yourself from falsehood” (Shmos 23:7) and does not relate it to a general principle that a judge may follow his intuition.

[6]Hilchos Sanhedrin 24:1-2, and see Shulchan Aruch C.M. 15:5.

[7]R’ Yitzchak Tzvi Ushinsky, Mechonas Emes Behalacha, Bais Hillel 23 (Tamuz 5765) p. 45.