Does Rabbi Yosei holds the principle אִיסּוּר חָל עַל אִיסּוּר? TB Yevamot 32

At first glance Rabbi Yosei seemingly contradicts himself. Two brothers, Reuvan and Shimon marry two sisters. Reuvan marries Rachel and Shimon marries Leah. Shimon dies and Reuvan marries Leah. Reuvan has violated two ’ervot prohibitions, having relations with his brother’s wife and at the same time his wife’s sister. “If he engaged in sexual intercourse with this woman who was forbidden to him, he is liable to receive punishment for violating the prohibition against marrying a brother’s wife, because she was never rendered permitted by the levirate mitzva, and he is liable to receive punishment for violating the prohibition against marrying a wife’s sister; this is the statement of Rabbi Yosei.” (Sefaria.org translation) Here Rabbi Yosei holds the principle “a prohibition takes effect where another prohibition already exists-אִיסּוּר חָל עַל אִיסּוּר”

Later on Rabbi Yosei holds the opposite position whatever transgression comes first is the one the culpable person is liable for. “The baraita indicates that Rabbi Yosei holds that if the brother consummated the levirate marriage with this woman he violated two prohibitions. The Gemara asks: And does Rabbi Yosei hold that a prohibition takes effect where another prohibition already exists? But isn’t it taught in a baraita: One who committed a transgression deserving of two death penalties is sentenced to the harsher of the two deaths? One would be guilty of such a transgression if he engaged in intercourse with a forbidden relative who was also a married woman, as he would incur one death penalty due to her being a forbidden relative and one death penalty due to her being a married woman. Rabbi Yosei says: He is sentenced according to the first relationship that applied to him with regard to this woman.”(Sefaria.org translation)

To solve this contradiction we have to understand two different terms. The first term is an expanded prohibition, אִיסּוּר מוֹסִיף.

“Rabbi Abbahu said: Rabbi Yosei concedes that a prohibition takes effect where another prohibition already exists when it is an expanded prohibition. An expanded prohibition is a prohibition that has a greater scope than the original prohibition, either because it applies with greater severity or because it applies to additional individuals. Rabbi Yosei holds that if the second prohibition incorporates additional individuals into the list of those for whom the original item is prohibited, then it takes effect in addition to the previous prohibition that had a more limited range.

“This works out well in cases where the living brother (i.e. Reuvan ) married his wife first, and her sister became forbidden to him as a wife’s sister, and then afterward the brother who was subsequently deceased married (i.e. Shimon) his wife’s sister. In that case it is possible to say: Since a prohibition was added for all the brothers, a prohibition was added for the living brother as well, and he is liable due to both prohibitions, as this prohibition is more wide-ranging than the previous one. In other words, at first this sister was permitted to the other brothers, and when the second brother married her she was rendered a brother’s wife and so she was additionally forbidden to the other brothers.” (Sefaria.org translation)

The second term is “a more inclusive prohibition- אִיסּוּר כּוֹלֵל.”

“However, where the deceased brother married first and afterward the living brother married her sister, in what way is there a prohibition that adds? No additional individuals were incorporated into the prohibition as a result of the marriage of the living brother with the sister, since the prohibition here proscribing a wife’s sister applies to him alone.

if you would say: Since he himself now married a sister he became prohibited to all of the other sisters, as opposed to the prior state of affairs where only his brother was married to one of the sisters and all of the other sisters were permitted to him, and therefore an additional prohibition now applies to him, this is difficult. In this case the new prohibition is not considered an expanded prohibition, but rather it is considered a more inclusive prohibition. It is more inclusive and more comprehensive in that it adds additional aspects to the prohibition for the same individual. This is not called an expanded prohibition, as it does not add prohibitions to additional individuals.” (Sefaria.org translation)

The sugiyah concludes by solving the contradiction completely differently. The person is only liable for one punishment; however, Rabbi Yosei ascribes to transgressions. “Rather, Rava said that when Rabbi Yosei stated in the baraita that the man is liable due to both prohibitions, for a brother’s wife and for a wife’s sister, he meant to say: I ascribe to him liability as though he transgressed twice, since indeed he violated two prohibitions, yet he is liable to receive punishment in human courts on only one count. And likewise, when Ravin came from Eretz Yisrael to Babylonia, he said that Rabbi Yoḥanan said: I ascribe to him liability as though he transgressed twice, yet he is liable to receive punishment on only one count.” (Sefaria.org translation)