Daf Yomi - Sukkah 39 - Mitzva Remnants

Tosfos rules that one who took the lulav and did not recite the blessing can still do so as long as he has not yet waved the lulav. Although one can fulfill the mitzvah of lulav without waving it, the mitzvah is not deemed to be complete until he waves the lulav. This follows the principle that one can recite a blessing for a mitzvah as long as he has not completed the mitzvah. Thus, one can recite the blessing of netilas yadayim after washing his hands because the mitzvah is not deemed to be complete until one dries his hands. The Pri Megadim writes that if one commenced lighting the Chanukah lights without reciting a blessing, he can still recite the blessing as long as he has not kindled all of the lights that are required for that particular night. Regarding Chanukah lights we also apply the rationale that although one essentially discharges his obligation by kindling one light, the subsequent lights are also deemed to be a part of the mitzvah. Thus, one who has not completed lighting all the lights for that particular night is deemed to be engaged in the mitzvah and he can still recite the blessing.