The day-year principle or year-for-a-day principle is a method of interpretation of Bible prophecy in which the word day in prophecy is considered to be symbolic of a year of actual time. It was the method used by most of the Reformers, and is used principally by the historicist school of prophetic interpretation. It is held by the Seventh-day Adventist Church, Jehovah's Witnesses, and the Christadelphians. The day-year principle is also used by the Baháʼí Faith, as well with by most all astrologers who employ the "Secondary Progression" theory, aka the day-for-a-year theory, wherein the planets are moved forwards in the table of planetary motion a day for each year of life or fraction thereof. The astrologers say that the four seasons of the year are directly spiritually, phenomenologically like the four "seasons" of the day.

In the Book of Revelation, the two witnesses are two prophets who are mentioned in Revelation 11:1-14. Some Christians interpret this as two people, two groups of people, or two concepts. Some believe they are Enoch and Elijah, as in the Gospel of Nicodemus, since they are the only two that did not see death as required by the Scriptures, while others believe them to be Moses and Elijah because they appeared during the transfiguration of Jesus, or because Enoch was not Abraham's descendant. They have the power to shut the heavens (Elijah) and turn water into blood (Moses).