John Gill Bible Commentary

Which was the son of Cainan,.... This Cainan is not mentioned by Moses in Gen 11:12 nor has he ever appeared in any Hebrew copy of the Old Testament, nor in the Samaritan version, nor in the Targum; nor is he mentioned by Josephus, nor in Ch1 1:24 where the genealogy is repeated; nor is it in Beza's most ancient Greek copy of Luke: it indeed stands in the present copies of the Septuagint, but was not originally there; and therefore could not be taken by Luke from thence, but seems to be owing to some early negligent transcriber of Luke's Gospel, and since put into the Septuagint to give it authority: I say "early", because it is in many Greek copies, and in the Vulgate Latin, and all the Oriental versions, even in the Syriac, the oldest of them; but ought not to stand neither in the text, nor in any version: for certain it is, there never was such a Cainan, the son of Arphaxad, for Salah was his son; and with him the next words should be connected, which was the son of Arphaxad; Gen 11:12 which was the son of Sem, or Shem, Gen 11:10 which was the son of Noe, or Noah, Gen 5:32 which was the son of Lamech,