Daf Yomi - Rosh Hashana 14 - COMPOUNDED DOUBTS

The Gemora cites an incident with Rabbi Akiva that he picked esrogim from a tree on the first of Shevat. He separated maaser sheini as if it was the second year of the Shemitah cycle and he also separated maaser oni as if it was the third year of the Shemitah cycle.

Rabbi Akiva was being strict regarding the halachos of separating maaser from the fruits of the tree. The commentators ask that separating maaser from fruits is only Rabbinic and the principle is that when there is a doubt on a Rabbinic law, one has a right to be lenient. Why did Rabbi Akiva choose to be strict?

The Shaar Hamelech in Hilchos Mikvaos cites Tosfos in Bava Kamma and based on Tosfos explains our Gemora. When there are two Rabbinic doubts that contradict each other, one cannot rule leniently on just one of them since who says that this is the correct one. We cannot rule leniently on both of them since they contradict one another. We are therefore compelled to rule stringently on both of them. It is because of this reasoning that Rabbi Akiva separated maaser for both years.