The practice of indicating, by different types, words, and phrases which were not in the Original Text, was, it is believed, first introduced by Sebastian Münster, of Basle, in a Latin version of the Old Testament published in 1534.

  The English New Testament (published at Geneva, 1557) and the Geneva Bible (1560) "put in that word which, lacking, made the sentence obscure, but set it in such letters as may easily be discerned from the common text." The example was followed and extended in the Bishops' Bible (1568, 1572), and the roman and italic¹ types of these Bibles (as distinguished from the black letter and roman type of previous Bibles) were introduced into the Authorized Version (1611).

  The following seem to have been the principles guiding the translators of the Authorized Version:—

1. To supply the omissions under the Figure of Speech Ellipsis, or what they considered to be Ellipsis.
2. To supply the words necessary to give the sense, when the Figure of Speech Zeugma is employed.
3. Once, at least, to indicate a word or words of doubtful Manuscript authority, 1John 2:23 (first introduced in Cranmer's Bible—doubtless from the Vulgate). Perhaps also Judges 16:2 and 20:9.
4. Where the English idiom differs from that of the Originals, and requires essential words to be added, which are not necessary in the Hebrew or Greek.

   For the use of italic in the Revised Version see Appendix 7.

  The use of large capital letters for certain words and phrases originated with the Authorized Version. None of the previous or "former translations" have them.

  The revisers abandoned this practice, but have not been consistent in the plan they substituted for it.
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  ¹ The word italic means relating to Italy, and is used of a kind of type dedicated to the States of Italy, by Aldus Manutius, about the year 1500.

In most of the cases they have used small capital letters instead of the large capitals; but in three cases (Jeremiah 23:6. Zechariah 3:8; 6:12) they have used ordinary roman type.
  The use of the large capitals by the translators of the Authorized Version is destitute of any authority, and merely indicates the importance which they attached to such words and phrases thus indicated.

  The following is a complete list:—

  Large capitals in A.V. Small capitals in R.V.

Exodus 3:14. "I am that I am."

Exodus 3:14. "I am."

Exodus 6:3. "Jehovah."

Exodus 28:36; 39:30. "Holiness (R.V. "Holy") to the Lord."

Deuteronomy 28:58. "The Lord thy God."

Psalm 68:4. "Jah."

Psalm 83:18. "Jehovah."

Isaiah 26:4. "Jehovah."

Daniel 5:25-28. "Mene, Mene, Tekel, Upharsin," (verse 28, "Peres".)

Zechariah 14:20. "Holiness (R.V. "Holy") unto the Lord."

Matthew 1:21. "Jesus."

Matthew 1:25. "Jesus."

Matthew 27:37. The inscriptions on the Cross. Also Mark 15:26. Luke 23:38. John 19:19.

Luke 1:31; 2:21. "Jesus."

Acts 17:23. "To the (R.V. "an") unknown God."

Revelation 17:5. "Mystery, Babylon the Great, the Mother of (R.V. "the") Harlots and (R.V. "the") Abominations of the Earth."

Revelation 19:16. "King of Kings, and Lord of Lords."
 

  Large capitals in A.V. Small roman letters in R.V.

Jeremiah 23:6. "The Lord our Righteousness."

Zechariah 3:8. "Branch."

Zechariah 6:12. "Branch."