And a new king arose on Mitzrayim who did not know Yosef (Shemos 1/8).
According to one opinion in Gemara Sotah, 11a, this possuk is not to be understood literally as, “A new king began to rule over Mitzrayim”, rather, the possuk tells us that the ruling king renewed his decrees (Hischadaish Gezairosov). Meaning, the old king who ruled during the times of Yosef acted AS IF he was a new king.
The Gemara asks, according to this, how can one understand the second half of the possuk, "... who didn't know Yosef"? The Gemara answers that he actually remembered Yosef but he acted as if he didn't remember him.
Zera Shimshon asks. What does it mean that Paroah "renewed his decrees"? From the pessukim it doesn't seem that Paroah reactivated old decrees that had lain dormant but rather he made new decrees against Bnei Yisroel, like making them build the cities of Pissom and Ramsais. We don't find that they in the past they built cities, so this was a new decree. Then what does Chazal mean when they say that Paroah “renewed his decrees”?
Secondly, all the Mitzriyim, and even the whole world, knew that Yosef ruled under Paroah. So what does it mean that Paroah made believe that he didn't remember him? If this would be made known to the public, he would have been the laughingstock of Mitzrayim and the whole world!
Even more so, if the intent of Chazal was that Paroah pretended that he did not remember Yosef, the possuk should have been written; “And a new king rose to power who did not remember Yosef” and not, “who did not know Yosef”!
Zera Shimshon's Explanation
Zera Shimshon answers these questions in the light of an idea found in Assara Maamoros. It was not incidental that Hashem orchestrated for Yosef to rule over Mitzrayim BEFORE the Mitzriyim ruled over Bnei Yisroel and enslaved them. Hashem chose to first have Yosef rule so he would acquire all of the Mitzriyim as slaves. Therefore, when Bnei Yisroel eventually were forced to work for the Mitzriyim they were not technically owned by them because of the halacha that says, "Whatever a slave owns, is owned by his master" (mah shekonno avdo kanno rabbo). Since the Mitzriyim belonged to Yosef, Bnei Yisroel also belonged to Yosef and his descendants!
However, if Yosef would not have bought all of the Mitzriyim, then later on Bnei Yisroel would have become real slaves to the Mitzriyim. Bnei Yisroel would have been so assimilated in the Mitzriyim's culture that they would not have been able to be redeemed and purified of their tumah.
Paroah understood all of this and he wanted to continue to rule over Bnei Yisroel for them do slave labor for him forever. The problem was, though, that they were not legally slaves and therefore Paroah understood that they would be redeemed so time or other. Therefore Paroah tried to challenge and invalidate the original rule of Yosef which would cancel Yosef's acquisition of the Mitzriyim that took place at the time of the great famine and Bnei Yisroel would legally belong to the Mitzriyim and like this they would never be able to be redeemed.
The idea that Paroah had to do this was to renew the old decree that a slave cannot rule over Mitzrayim and to say that this law applies to Yosef who was called a slave. Like it is written; and there, with us, was a Hebrew person, a slave to the master of the butchers. This is the decree that Paraoh renewed.
Paroah's plan, though, was foolish because after Yaakov and the Shevatim came down to Mitzrayim, everyone knew that Yosef was really not a slave, but simply kidnapped from his land. Therefore, according to Egyptian law, Yosef was suitable to be a ruler and he legally owned all of the Mitzriyim.
According to this, the intent of Chazal, who said that Paraoh made himself as if he did not know Yosef, is not that Paraoh pretended that he didn't remember who Yosef was, rather, he pretended as if he was really a slave, and not a free person, and therefore was not able to be a ruler in Mitzrayim.
However, it is still unclear why the Mitzriyim would believe that Yosef was really a slave after they saw, when Yaakov came down to Mitzrayim, that he called Yosef “my son”, which proves that he was kidnapped from his land and therefore not a slave.
We can answer this question in the light of the Halacha that is written in Babba Basra. A person, who says that a specific boy is his son, is believed and cannot retract this testimony. However, the Shulchan Aruch paskens, that the father is not believed in every situation. If there is a personal benefit to the one testifying, for instance he will be exempt from some type of tax, the father is not completely believed and he is able to retract his testimony.
Therefore, Paroah claimed that Yosef really was a slave, like everyone thought before Yaakov and the Shevatim came down to Mitzrayim. The fact that Yaakov call Yosef his son is not a good proof against this because Yaakov might of said it only in order to be able to get food during the famine. Therefore, Paroah argued that Bnei Yisroel are really slaves and there is no way for them to go free.
