Reprinted with permission from The JPS Guide to Jewish Traditions, published by the Jewish Publication Society.
The honor of reciting the blessings over the Torah is called an aliyah (plural, aliyot), which means “going up.” This refers both to the physical ascent of the person to the bimah where the Torah is read and to the spiritual uplifting associated with participation in this hallowed ritual.
The number of aliyot varies widely (Meg. 4:1-2). Three people are called to the Torah on Monday and Thursday mornings, on Sabbath afternoons, during the mincha service on Yom Kippur, on the festivals of Hanukkah and Purim, and on all fast days.
Among the reasons offered for this ruling are the three classes of Jews (Kohanim, Levites, Israelites) that must be represented; the threefold division of the Bible (Torah, Prophets, Writings); and the threefold Priestly Blessing, the first of which contains three Hebrew words (Meg. 21b). On Monday and Thursday mornings, when congregants have to go to work, calling up more than three people would overly lengthen the service. If there were more than three aliyot at Mincha on Saturday afternoon, the service would not be completed before dark (Rashi, Meg. 21a).
Each aliyah must consist of a minimum of three verses (Meg. 4:4), and a public Torah reading must have a minimum of 10 verses (Meg. 21b)–a practice traditionally related to the number of commandments in the Decalogue. The only exceptions to this practice are the reading for Purim morning (Exod. 17:8-16) and the weekday reading for the section of Vayelekh (Deut. 31:1-9), when a total of nine verses are read.
Number of Aliyot
There are four aliyot on Rosh Hodesh and on the intermediate days (hol hamoed) of Passover and Sukkot; five on Rosh Hashanah and on the festival days of Passover, Shavuot, and Sukkot; six on the morning of Yom Kippur; and seven on Sabbath morning.
On Sabbath mornings, some congregations take advantage of a provision in Jewish law that permits dividing the Torah portion into more (but not less) than the required number of aliyot (Meg.23a). This is not permitted on Mondays or Thursdays or when Rosh Hodesh, Hanukkah, and fast days fall during the midweek, lest it waste the time of people who must go to work (bittul melakhah).