Mitzvot Tzrichot Kavana - Minchat Shlomo O.C. 1

 In this teshuva, Rav Shlomo Zalman Auerbach deals with the question of whether or not doing a mitzva without kavana invalidates the performance of that mitzva.  Specifically, he wonders whether someone who eats in a succah but lacks kavana for the mitzva is considered to have eaten outside of the succah, or if someone who wears tzitzit without having kavana for the mitzva is considered as if he failed to wait tzitzit on that garment.  Along the way, he raises further possible ramifications, such as whether one would violate the prohibition of kilayim if he wore wool tzitzit on a linen garment (which is normally permitted for the mitzva) without having kavana to fulfill the mitzva.  After analyzing the question through the perspective of other mitzvot, such as affixing a mezuza to one's door, slaughtering an animal, and putting a fence around one's roof, Rav Auerbach concludes that while one who wears tzitzit without having kavana for the mitzva does not fulfill the mitzva, he also does not violate a lo ta'aseh, where one who sits in a succah with having kavana for the mitzva may be in violation of something since there is the additional requirement of teishvu k'ein taduru.

In the second section of this teshuva, Rav Auerbach determines that if one loses kavana during a mitzva he can still fulfill the mitzva.  His main focus is on someone who is saying Shema or Shemoneh Esrei and his mind wanders.  While he wants to say that it does not count, based on the halacha that someone who is not sure which u'chtavtam he is up to can continue with Shema if he instinctively says l'ma'an yirbu (since we assume that that is where he was up to), he infers that it counts at least b'diavad.  However, if someone is listening to someone else make a bracha or say a tefilla, he can only fulfill his obligation if he listens to the entire thing.

Leishev BaSuccah - Yechaveh Daat 5:48

Can one make a bracha of לישב בסוכה if one is already in the middle of his meal? Rav Ovadiah Yosef deals with this question and comes out with a very interesting psak.

With regards to the main question, even though the mitzva of sitting in the succah includes all types of actions, since we have established that the bracha is said only when one eats there, then once one has concluded his meal he can no longer make the bracha. However, if one is still in the middle of his meal, then even though ברכות המצוה generally need to be said עובר לעשייתן - before the performance of the mitzva - nevertheless Rambam rules (Hil. Brachot 11:5) that one can still make the bracha so long as he is still in the midst of performing the mitzva.

Rav Yosef moves from there to note that even if one is no longer eating bread, he can still make the bracha even if he is eating foods that would not require the bracha if they were eaten independently, such as fruits. The rationale for this is that since they have become part of the meal, they can be used as a lever for making the bracha on the entire meal.

Rav Yosef then makes an intriguing move. Normally the halacha is that one does not need to make a bracha on certain foods since they are normally eaten in an עראי (casual) manner. However, if one were to be eating such foods in the middle of a meal, then the eating of those foods, even including a drink of water, would be transformed into אכילת קבע, a more established form of eating, and thus it would be forbidden to eat any part of the meal outside of the succah.