Commandments · Negative commandments

Not to have sexual relations with one's sister

#488 Negative commandment Leviticus 18:9

The cited verse

The Hebrew (Masoretic Text)

עֶרְוַת אֲחוֹתְךָ בַת־אָבִיךָ אוֹ בַת־אִמֶּךָ מוֹלֶדֶת בַּיִת אוֹ מוֹלֶדֶת חוּץ לֹא תְגַלֶּה עֶרְוָתָן

In Maimonides’ words

How Maimonides defines this commandment in his Sefer HaMitzvot — his own words, shown as a primary source.

הזהיר מגלות ערות אחותו. והוא אמרו ערות אחותך בת אביך או בת אמך לא תגלה ערותן, והעובר על לאו זה במזיד חייב כרת ובשוגג יקריב קרבן חטאת קבועה:

He prohibited sexual intercourse with the sister. And that is His saying, "The nakedness of your sister, your father's daughter or your mother's daughter [...] - you shall not uncover their nakedness" (Leviticus 18:9). And one who transgresses this negative commandment volitionally is liable for excision. But if it was inadvertent, he must sacrifice a fixed sin-offering.

Hebrew: Sefer HaMitzvot, Warsaw 1883 (public domain). English: Sefaria Edition, trans. Rabbi Francis Nataf, 2021 (CC0). Via Sefaria; translator’s footnotes omitted.

Literary form: a prohibition

Applicability

How the catalog describes where and when this commandment applies. These are independent descriptions, not a verdict on which laws still count.

  • Recorded as practiced today

Classical halakhic consequences

The consequences the classical halakhah attaches to this commandment, grouped by who imposes them. Where a category has none recorded, that absence is itself meaningful.

Imposed by a court

  • Lashes (malkot)

At the hands of Heaven

  • Karet — being 'cut off'

Ritual remedy

  • A sin-offering (ḥatat)

How the streams of Judaism treat this commandment

The streams of Judaism read the same commandment differently — an ongoing plurality, not a ranking. Each position below is reported as the catalog records it; none is presented as the correct one.

  • Orthodox Binding
  • Conservative Binding
  • Reform Kept as an ethical principle
  • Reconstructionist Kept as an ethical principle
  • Karaite Binding

24 of 613 commandments have been examined in depth so far — this one is queued.

How later traditions received this commandment

How later traditions read or reworked this commandment, each attributed to its own voice. The catalog’s own classification of each reception is shown as it records it, never adopted as GEBible’s.

Qumran (the Dead Sea Scrolls)

  • 4QMMT / CD treatment of Lev 18 'arayot (general) read it more strictly

Rabbinic aggadah

  • Genesis Rabbah 18:5 expanded it homiletically

Philo of Alexandria

  • De Specialibus Legibus 3.22-25 rationalized it

Josephus

  • Ant. 3.274-275 affirmed it

The Qur'an and hadith

  • Q 4:23 carried a parallel

Beside the older legal codes of its world

The commandment set beside the ancient Near-Eastern legal collections scholars compare it to — a descriptive comparison, not a claim of dependence.

  • hittite laws consanguine incest list (mother, daughter, son) — sister conspicuously absent Relationship to the parallel: parallel with divergence §189 Roth, Law Collections from Mesopotamia and Asia Minor, 2nd ed. (1997)
  • hittite laws free man with mother+daughter+sister cluster conditioned by geographic distinctions Relationship to the parallel: parallel with divergence §191 Roth, Law Collections from Mesopotamia and Asia Minor, 2nd ed. (1997)
  • code of hammurabi father-daughter incest punished by banishment (sibling incest not addressed) Relationship to the parallel: parallel with divergence §154 Roth, Law Collections from Mesopotamia and Asia Minor, 2nd ed. (1997)

Where this commandment meets modern human-rights frameworks

One modern normative lens, attributed to it — not GEBible’s assessment. Each row names the framework it measures against and the catalog’s own classification of the relation.

This framework catalogues tensions; it records agreement in only one of its entries. The near-total tension rate is the shape of the instrument, not a finding.

No tension with the catalogued modern frameworks is recorded here.

Source & licence

The commentary, cross-references, reception, and modern-conflict analysis in this section are drawn from a public compilation of the 613 commandments, licensed under CC BY-SA 4.0. The cited biblical text is rendered from GEBible’s own public-domain reading corpus. CC BY-SA 4.0 (opens in a new tab). GEBible’s presentation of this material is offered under the same CC BY-SA 4.0 terms.