The proper delineation of the Ten Commandments is known when Kabbalah is understood. Each sephirah has properties related to it, and the 6th matches Thou Shalt Not Fornicate. Those who don't understand this end up grouping different phrases and sentences to the wrong commandment.

Thou Shalt Not Fornicate is 6 because it relates to Tiphereth, the Arcanum 6, etc.