On yesterday’s daf (=page) the Gemara presented a disagreement between Rav and Shmuel regarding the status of the turbatz ha-veshet, the animal’s pharynx. This area, which is where the esophagus enters the throat, is considered by Rav to be a place where ritual slaughter can take place, while Shmuel rules that it is too high up in the animal’s throat to be an appropriate place for slaughter. When a practical situation of shehitah in this area was brought before Rava, he applied both Rav’s position and Shmuel’s position to rule stringently in that case.
The halakhah is always in accordance with the ruling of Bet Hillel. Nevertheless one who desires to adopt the view of Bet Shammai may do so, and one who desires to adopt the view of Bet Hillel may do so. One who adopts the view of Bet Shammai only when they incline to leniency, and likewise the view of Bet Hillel only when they incline to leniency, is a wicked person. One who adopts the view of Bet Shammai only when they incline to strictness and likewise the view of Bet Hillel only when they incline to strictness, is a fool and to such an one applies the passage in Kohelet (2:14): ‘But the fool walketh in darkness.’ But one must either adopt the view of Bet Shammai in all cases, whether they incline to leniency or strictness, or the view of Bet Hillel in all cases, whether they incline to leniency or strictness.
In fact, this baraita should not be understood to mean that a person may never choose to be stringent by following two different opinions, since we find general principles of halakhic rulings – e.g. ‘regarding biblical questions follow the stringent view; regarding rabbinic questions follow the lenient opinion,’ see Avodah Zarah 7a – that may lead to such conclusions. It is only in situations where the stringency stems from the application of two rulings that stand diametrically opposed to one another that the person who adopts both is considered to be behaving foolishly. Rava’s ruling clearly fell into that category.