Tahanun (תַּחֲנוּן) or “supplication” is also sometimes called “nefilat appayim,” which means “falling on the face.” It is a part of the morning (Shaharit) service and also the afternoon (Minhah) service, falling just after the Amidah. Differing practices have arisen around this prayer which has its roots in the Bible and is set forth in the Talmud (see below). In fact, it has been with us longer even than the Kaddish. Tahanun is a confession of sins and petition for grace, and was originally recited prostrate on the ground. It is a bit of Yom Kippur on a daily basis.
The short Tahanun begins with verses from II Samuel (24:14), “let us fall, I pray, into the hand of the Lord, for His mercies are many, but let me not fall into the hand of men.” It continues with Psalm of David (6:2-11) in which David describes his pain. If a Sefer Torah is present, one follows the Shulhan Arukh (Orakh Hayim 131:1-2) and leans one’s head on the back of one’s left hand or arm (or right arm if there are tefillin on the left). The poem Shomer Yisrael (which also may be found at Selihot) is recited seated but at attention. (Some congregations sing it.) Composed with increasing line length and complexity, embedding the Shema, the poem asks God to remember our use to him, while also reminding us to comport ourselves accordingly. In some traditions, then, all rise for the ending, which is followed by Kaddish. (At Beth Shalom, we do not rise.) There is a long Tahanun as well, done on Mondays and Thursdays, beginning with personal reflection and including more Psalms and possibly Daniel 9:15.
The origin of Tahanun is Daniel 9:3 and I Kings 8:54, which both indicate that prayer should be followed by supplication. It is outlined in the Babylonian Talmud, Berakhot 16b. One drops one’s face on one’s hand in reference to the line “let us fall into the hand of God.” The practice also recalls the daily sacrifice at the Temple which would have been laid on its left side to be slaughtered. The need for the presence of a Sefer Torah is based on tradition deriving from Joshua falling on his face before the Ark of the Covenant. It is believed to have been solidified into the modern form in the 16th century, as prior prayer books varied in its expression.
We omit Tahanun (and any part of it) on festive days and mournful days: Shabbat, all holidays and festivals including Hol haMoed, Rosh Hodesh, the day before Yom Kippur, from Simhat Torah through the end of Tishrei, from the beginning of Sivan through Shavuot, the month of Nisan, Tu BiShevat, Purim Katan, Shushan Purim Katan, Shushan Purim, Lag BaOmer, Tisha BeAv, Tu BeAv (only at Shaharit), the day before Rosh Hashanah, and when observing any festive or solemn rites of passage. Some also omit Tahanun on Adar 23-29 (remembering the days before the inauguration of the Mishkan), Pesah Sheni (we shall do a column about that observance), and Sivan 7-12 (remembering the day after Shavuot plus a week during which an offering would have been brought to the Temple).
We need a chart on the wall just to know whether we can say it!