Eid Echad Ne'eman B'Isurin: Fact or Presumption?

This shiur addresses a fundamental machloket in understanding the nature of eid echad ne'eman b'isurin. According to the Ramban (רמב"ן)'s approach presented earlier, eid echad in isurim establishes a fact (din d'vaday). This allows eid echad to negate a chezkas isura when combined with certain conditions: it must involve yado (the witness's own action making it less valuable), the witness must be ne'eman on himself, or the chezkas isura must not be applicable. In contrast, Tosfos understands eid echad ne'eman b'isurin not as establishing fact but as creating a presumption—enough to remove the din of safek d'Oraisa l'chumra without being an absolute fact. There is no safek requiring stringency, but neither is there certainty. The shiur then analyzes the Rambam (רמב"ם)'s presentation in Hilchos Eidus. In Perek Hei, the Rambam states that no din can be decided based on eid echad, neither in capital cases nor monetary cases, citing "lo yakum eid echad b'ish." The Rambam lists two exceptions where the Torah (תורה) explicitly accepts eid echad: sotah, eglah arufah, and eidus on death (isha). He adds that wherever eid echad is effective, even a woman or pasul witness is valid, except for shevuah, which requires a witness who is "ra'ui l'tzaref" (fit to join with another). Logically, the Rambam should have mentioned eid echad ne'eman b'isurin in this perek as another exception to the two-witness requirement. Instead, he places it much later in Perek Yud Alef, halacha (הלכה) zayin, stating that eid echad is believed regarding isurim even if the witness is pasul for other eidus, such as a woman who forgot her shechitah being believed to say "I slaughtered properly." However, one who is chashud on a matter cannot testify about it, though he can testify about other matters.