A Hebrew word meaning “certainly” or “may it be so.” In the Hebrew Bible amen appears as a response to someone else's statement. Sometimes it appears in a liturgical setting as a response of the people (Deut. 27.15–26; Ps. 106.48), sometimes as a solemn response to another person's statement (1 Kings 1.36; Jer. 28.6 [an ironic response]), sometimes as a response to God's word (Jer. 11.5). The doubled form, amen, amen (Num. 5.22; Neh. 8.6) also occurs; compare “amen and amen” (Ps. 41.13). Amen may be used as a substantive: “the God of amen” = “the God of faithfulness” (Isa. 65.16); this meaning is reflected in the New Testament (Rev. 3.14).

The Hebrew amen was retained among early Greek‐speaking Christians as a confirmatory response to prayer, whether one's own (Rom. 16.27) or someone else's (1 Cor. 14.16). This continues in Christian liturgical usage.

In the speech of Jesus in the Gospels, amen often appears not as a closing response but as an opening affirmation of the validity and seriousness of what follows: “Amen (‘Truly’) I tell you …” (Matt. 5.18). In the Gospel of John, the amen that frequently introduces Jesus' speech is doubled: “Amen, amen (‘Truly, truly’ [NRSV: ‘Very truly’]) I say to you …” (John 1.51; etc.). The opening amen indicates the solemn claim of the speaker to authority. Many scholars see in this introductory amen a clear reflection of Jesus' sense of his own authority. The introductory amen was not completely new in the words of Jesus, however; there are a few instances of similar speech in contemporary sources. It is possible, however, that the language of early Christian worship influenced these passages.

William A. Beardslee