Let us briefly review the three approaches to the nature of the exemption of the onen that are found in the Shulchan Aruch.

1) In Orach Chayyim 71:1, Rav Yosef Karo says that the onen is exempt and prohibited when directly involved with burial preparations. However, if there are people to care for the physical needs, we do not stop the onen from performing Mitzvot (“exempt but permitted”). This is the approach of R. Yitzchak quoted in Tosafot on the page (Berachot 23b s.v. v’ein mevarvhin alav and Or Zarua Section 2, Hilkhot Aveilut siman 417) as well as referred to by the Rosh (Berachot 3:1 & Moed Katan 3:54).

2) The first position brought anonymously in Yoreh Deah 341:1 is that the onen is exempt from all positive Mitzvot but is permitted to perform them. This is the opinion of Rashi (Berachot 17b s.v. vi-ein mevarech) and Rambam (Rambam Hilkhot Avel 4:6 and Hilkhot Kriyat Shema 4:7).

3) The second approach in Yoreh Deah 341:1, introduced with the phrase “יש אומרים – some say”, is that the onen is exempt and prohibited from performing all positive Mitzvot. This is the majority position of Tosafot (Berachot 17b s.v. vi-ein mevarech), Ra”ah (Berachot 16b s.v. mi she-meito mutal) Rosh (Berachot 3:1) and Talmidei Rabbeinu Yona (Rif, Berachot page 10b). 

This chart might be a helpful way to see the three different approaches that appear in the Shulchan Aruch:

Orach Chayyim 71:1	Exempt and prohibited when involved with  burial preparations; exempt and “we don’t stop the performance” (permitted) when others are involved
Yoreh Deah 341:1 (a) סתם	Exempt and permitted
Yoreh Deah 341:1 (b) י”א	Exempt and prohibited

This question has bothered commentators on the Shulchan Aruch for nearly 400 years. In the first half of the 17th century (within about 100 years of the publication of the Shulchan Aruch), there were four significant attempts to deal with this apparent contradiction.

Rabbi Mordechai Yaffeh¹points out the problem, but he simply does not understand Rav Yosef Karo at all. The Levush is so committed to the idea that the main concern is one of giving honor to the departed loved one that he does not even try to harmonize the many positions brought in the Shulchan Aruch². Since the main reason for the exemption from positive Mitzvot is that the mourner should be focusing their attention and thoughts on their loved one, the support from the community in terms of the details of the burial is irrelevant.

Rabbi Yom Tiv Lippman Heller³ is so bothered by this contradiction that he emends the text⁴ in Orach Chayyim so that Rav Yosef Karo now paskens like Tosafot and the onen is exempt and prohibited.

Rabbi David ha-Levi Segal⁵after noting the contradiction, claims that Rav Yosef Karo paskens like Yoreh Deah against Orach Chayyim. He, like the Levush, assumes that the concern for honor due to the one who has passed needs to be taken into consideration and therefore it is better to remain passive⁶ and not fulfill positive commandments.

Rabbi Gershon Ashkenazi⁷is committed to harmonizing the two seifim of the Shulchan Aruch. He understands that when Rav Yosef Karo in Orach Chayyim says first that it is forbidden to be stringent on reciting blessings, that is what he really thinks. However, if someone does so, we are not required to stop them (איו מוחין) even though their action is forbidden.

In the final analysis, how the early achronim understand the Shulchan Aruch is heavily influenced by their assumptions about the Yerushalmi that we unpacked two weeks ago (see this link). If the core explanation for the exemption from Mitzvot is about the appropriate honor due to the one who has passed (כבוד המת) then the Onen basically remains exempt and likely prohibited almost regardless. When people shift towards the idea of the exemption being about taking care of the physical needs and preparations for the burial (ישא משאו) there is more room for flexibility.

  

1. Levush haTechelet 91:1
2. See the the Ra”ah at the beginning of the third chapter of Berachot, which also appears in the Shita Mekubetzet, who clearly explains that doing Mitzvot is a distraction from the correct focus of the mourner, which is meant to be entirely on the one who had passed
3. Lechem / Divrei Chamudot on the Rosh 3:1 in Berachot note #2. He repeats his approach in his commentary on the Levush called the Malbushei Yom Tov 91:1. See also the Elya Rabba there note #2.
4. He adds a י”א into the Shulchan Aruch in Orach Chayyim so that the concluding sentence reads, “וי”א אם יש לו מי שישתדל בשבילו.”
5. Taz Orach Chayyim 91:3
6. שב ואל תעשה עדיף
7. Avodat ha-Gershuni siman 62, begins with a summary of the rishonim that I found very helpful and then notes the contradiction of the Shulchan Aruch. His approach is quoted by Rebbi Akiva Eiger in Orach Chayyim 71 in his gilyon on the Magen Avraham #2. The Shach quotes the Avodat haGershuni on a number of occasions. In Yoreh Deah 98:2 he even refers to Rav Gershon Ashkenazi as his ‘mechutan’ though the relationship remains unclear