Two of each animal, or seven pairs? Genesis 6 vs Genesis 7

The passages

And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female.

Genesis 6:19

Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.

Genesis 7:2

And the flood was forty days upon the earth.

Genesis 7:17

And the waters prevailed upon the earth an hundred and fifty days.

Genesis 7:24

The problem

In Genesis 6 Noah takes two of every kind. In Genesis 7 he takes seven of the clean animals and two of the unclean. The flood runs forty days in 7:17 and 150 days in 7:24. The story also uses two divine names, "God" in some verses and "the LORD" in others, and tells of the sending out of a raven and a dove in a way that seems to double a similar episode. The repeats and differences are close together in a short space.

What believers and scholars say

Elaboration, not contradiction. Many conservative readers see the second passage as adding detail to the first. Two is the minimum for every kind, and seven pairs is the instruction for the animals suitable for sacrifice (which Noah offers in 8:20). The 40 days of rain and the 150 days of rising water are two phases of the same event.

Two sources interwoven. In the classical view of the documentary hypothesis, the flood is the clearest example of a story assembled from two earlier versions, one using "God" (Elohim) and one using "the LORD" (YHWH). Each version had its own count of animals and its own timeline. Supporters can separate the strands and read each as a coherent story. Baden and Friedman present this case in different forms.

Literary doubling. Some scholars, such as Cassuto, accept the repetition but explain it as deliberate artistry, such as the repetition of a motif for emphasis, and not as evidence of sources.

Where this leaves it

Whether the doubling is harmony or seam depends on how much one expects of an ancient editor. Both readings can handle the details, but the source-critical reading handles them without adding assumptions. The first reading handles them by explaining each difference separately.