In a minyan, why do we need six people who are fasting for the Fast of the 17th of Tammuz to change the service?

Great question! This touches on the intersection of communal prayer, ta'anit tzibur (public fast), and the laws of tefillah (prayer) on fast days.

Key Takeaways

On a public fast day, the prayer service includes additions such as Selichot, the Aneinu blessing, and a Torah reading — but only when a sufficient number of fasters are present in the minyan.
The Shulchan Aruch requires that six out of ten men in the minyan be fasting for the full fast-day service to be recited.
This threshold of six represents a rov (majority) of the minyan, ensuring the communal character of the fast is genuinely present.
The 17th of Tammuz is a ta'anit tzibur (communal fast) ordained by the prophets, which triggers these special prayer requirements.
If fewer than six are fasting, the service reverts to a regular weekday service without the fast-day additions.

The Source of the Requirement

The Fast of the 17th of Tammuz as a Rabbinic/Prophetic Fast

The 17th of Tammuz is one of four fasts mentioned in Zechariah 8:19:

"כֹּה־אָמַר יְהֹוָה צְבָאוֹת צוֹם הָרְבִיעִי..." — "Thus says the Lord of Hosts: The fast of the fourth [month], the fast of the fifth, the fast of the seventh, and the fast of the tenth shall be for the House of Judah joy and gladness and happy festivals." [Zechariah 8:19]

The Mishnah in Ta'anit 4:6 records five calamities that occurred on the 17th of Tammuz:

"בְּשִׁבְעָה עָשָׂר בְּתַמּוּז נִשְׁתַּבְּרוּ הַלּוּחוֹת, וּבָטַל הַתָּמִיד, וְהֻבְקְעָה הָעִיר, וְשָׂרַף אַפּוֹסְטֹמוֹס אֶת הַתּוֹרָה, וְהֶעֱמִיד צֶלֶם בַּהֵיכָל" "On the 17th of Tammuz: the Tablets were broken, the daily offering (tamid) was abolished, the city wall was breached, Apostomos burned the Torah, and an idol was placed in the Sanctuary." [Mishnah Ta'anit 4:6]

Because it is a ta'anit tzibur — a communal fast — it has specific communal prayer requirements that don't apply to private fasting.

The Rule of Six Fasters

The Halachic Source

The requirement of six fasters comes from [Shulchan Aruch, Orach Chaim 566:3] (from your training knowledge, as this is not among the retrieved sources):

If there are six or more fasting in the minyan, the shaliach tzibur (prayer leader) recites Aneinu as a full separate blessing (between Goel Yisrael and Refaeinu) during Shemoneh Esrei, and the Torah is read. If fewer than six are fasting, Aneinu is recited only as an addition within the Shema Koleinu blessing, not as a standalone blessing.

Note: The rule of six is drawn from the halachic literature; the retrieved sources above do not directly address this specific number.

Why Six Specifically?

The number six out of ten is significant for two reasons:

Majority (Rov): Six constitutes a clear majority of the ten-man minyan. For the fast to be considered a communal fast in practice — not merely an individual one — the majority of those present must be participating in it.
The Principle of Lo Titgodedu ("do not divide into factions"): The community should not appear split, with some observing a fast-day service and others not. A majority of fasters gives the gathering a unified communal character.

The Mishnah Berurah (566:17, Rabbi Yisrael Meir Kagan, the Chofetz Chaim) explains that the six-person threshold ensures the prayer takes on a genuine tzibur (communal) character, since without a majority of fasters, it is as though no communal fast is occurring in that minyan.

Practical Halachic Differences Based on the Count

| Number Fasting | Status of Aneinu | Torah Reading | |---|---|---| | 6 or more | Full separate blessing by shaliach tzibur | Yes | | Fewer than 6 | Added within Shema Koleinu (individual only) | No (for the minyan) | | Individual fasting alone | Personal addition in Shema Koleinu | No |

An individual who is fasting always adds Aneinu privately within Shema Koleinu, regardless of how many others are fasting [Shulchan Aruch, Orach Chaim 565:1].

Broader Significance

This rule reflects a deep Torah principle: communal prayer and communal suffering have a different halachic weight than individual practice. The Talmud in [Ta'anit 11a] teaches that one who separates himself from the community in its time of distress does not merit to see its consolation. The fast-day service is specifically designed as a communal act of teshuva (repentance) and petition — and it only takes on its full liturgical form when the community is genuinely, majorly engaged in it.

For personal guidance on fast-day observance and prayer, consult your local rabbi or posek.