“I John, who also am your brother, and companion in tribulation, and in the kingdom and patience of Jesus Christ, was in the isle that is called Patmos, for the word of God, and for the testimony of Jesus Christ.” (Revelation 1:9, KJV)
The charge is that “also (και)” entered the Textus Receptus due to Erasmus’ mistranscription. Hoskier, however, identifies the Textus Receptus reading in the Ethiopic version. Josef Hofmann, who translated the Ethiopic into Latin, recognized that the Ethiopic is based on a very good Greek text.
Even supposing that και was not based on any Greek manuscript evidence, it would be unfair to denigrate the King James Version based on the inclusion of this one word. In 1 Thessalonians 2:10, the NKJV and ESV insert “also” and the NASB and NIV insert the equivalent “so is” despite the lack of Greek support. In 3 John 1:12, the NKJV, ESV and NIV insert “also”, again, despite the lack of Greek support. There is nothing false expressed by the inclusion of “also” in Revelation 1:9. John first says in Revelation 1:1 that he is a servant of God. Then in Revelation 1:9 John says he is “also” brother and companion. The inclusion of “also” makes sense structurally and semantically and causes no harm to the meaning of the text whatsoever even if it is an addition.
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Hoskier, H.C., Concerning The Text Of The Apocalypse, vol. 2 (1929) at p. 37.
Metzger, Bruce M., The Early Versions of the New Testament: Their Origin, Transmission and Limitations (1977) at p. 237.