1 tc The Byzantine text, almost alone, lacks the last eight words of this verse, “The person who confesses the Son has the Father also” (ὁ ὁμολογῶν τὸν υἱὸν καὶ τὸν πατέρα ἔχει, Jo Jomologwn ton Juion kai ton patera ecei). Although shorter readings are often preferred (since scribes would tend to add material rather than delete it), if an unintentional error is likely, shorter readings are generally considered secondary. This is a classic example of such an unintentional omission: The τὸν πατέρα ἔχει of the preceding clause occasioned the haplography, with the scribe’s eye skipping from one τὸν πατέρα ἔχει to the other. (Readings such as this also suggest that the Byzantine text may have originated [at least for 1 John and probably the general epistles] in a single archetype.)
