- Question: [Monday, 1st Elul 5781]
During Hallel on Rosh Chodesh I absentmindedly forgot to skip the paragraphs of Lo Lanu and Ahavti, and remembered only after I finished saying the paragraph of Ahavti. What am I supposed to do now?
In such a case you should skip the paragraph of Mah Ashiv and go straight to the verse of Halelu Es Hashem Kol Goyim. If you remembered only by the paragraph of Min Hameitzar, then you should skip some of that paragraph. If you did not remember until you already finished Hallel [or after having already reached Yehalelucha Hashem], you nonetheless fulfill your obligation and do not have to repeat it.
Explanation: The reason we skip paragraphs during Hallel of Rosh Chodesh is because the entire saying of this Hallel is due to mere custom and not a rabbinical institution, and in order to emphasize this and its contrast to the Hallel’s that are actually obligatory, we say what is called as “half Hallel.” Now, regarding the paragraphs that are to be skipped for this purpose, there is no set obligatory Halacha in this matter, and it just happens to be that the custom of Jewry was to choose to skip the paragraphs of Lo Lanu and Ahavti for reasons that are more unknown than understood. Thus, in the event that one did not skip these paragraphs then he should simply skip other paragraphs for the sake of emphasizing its non-obligatory state. However, in truth, even if one did not skip anything he certainly fulfills his obligation.
Sources: See Avnei Yashfeh O.C. 83:1; Rav A”C Naah in Yagdil Torah 4:1676; See regarding the general law and reason for saying the half Hallel: Michaber 422:2; Admur 488:3; 490:7; Tur 422; Taanis 28b; Levush 422:3; Kaf Hachaim 422:23; See regarding skipping the paragraphs of Lo Lanu and Ahavti: Siddur Admur; Tur 422; Rambam Chanukah 3:8; Elya Raba 422:12; Binyamin Zev 361; Hashlama Taanis 28b; Hamichtam Sukkah 44b; Koveitz Moriyah 34:4 Elul 5775 in great length; See Biur Halacha 422:6 “Lemafreia” based on Rambam Chanukah 3:8 that in truth one can skip which area he desires, however the above areas of skipping is the accepted custom..