Duration of the Egyptian Exile/2

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The Duration of the Egyptian Exile

Exegetical Approaches

Overview

Faced with the apparent contradictions between the explicit verses which speak of 400 or 430 years and the upper limit of 350 years derived from Moshe’s genealogy, different commentators chose to take some verses at face value while reinterpreting others. This yields a full spectrum of approaches regarding the total number of years the Israelites spent in Egypt.

Shadal and the Hoil Moshe maintain that the Children of Israel were in Egypt for the full 430 years. They propose that Moshe's genealogy omits several generations and includes only the more prominent personalities. Others view Moshe's genealogy as a full listing and therefore suggest that the nation was in Egypt for much less than 430 years. To do so, they reread the verses which speak of 430 or 400, suggesting that this time span does not begin with the descent to Egypt but with some other event such as Avraham's journey to Israel, the Covenant of the Pieces, or the birth of Yitzchak. Depending on which of these approaches is chosen, the Children of Israel might have been in Egypt anywhere between 210 and 240 years. There is also a compromise approach which suggests that though the original plan was for a full 400 year exile in Egypt, Hashem changed his mind and shortened the stay.1

Full 430 Years

The Israelites lived in Egypt for a full 430 years.

Crux of the position – Shadal and the Hoil Moshe maintain that the Israelites were in Egypt for a full 430 years. To do so, they must posit that Moshe's genealogy in Shemot 6 omits several generations and includes only the more prominent personalities.
430 years in Egypt – This position reads the verses in Shemot 12:40-41 literally, and thus maintains that the Israelites really were in Egypt for a full 430 years.
Moshe's paternal lineage – Shadal and the Hoil Moshe need to offer a novel interpretation of Shemot 6, maintaining that Moshe's genealogy omits several generations and includes only the more prominent personalities.5 Thus it, too, covers a period of 430 years.6
Moshe's maternal lineage – The Torah records that Yocheved was Levi's "daughter born to him in Egypt" ("‏בַּת־לֵוִי אֲשֶׁר יָלְדָה אֹתָהּ לְלֵוִי בְּמִצְרָיִם") and Amram's aunt ("דֹּדָתוֹ"‎).7 If so, Yocheved would need to have lived at least from the year of Levi's death until Moshe's birth, which would make her at least 256 years old when she gave birth to Moshe. Thus, in order to sustain his position, the Hoil Moshe is forced to interpret "בַּת־לֵוִי אֲשֶׁר יָלְדָה אֹתָהּ לְלֵוִי" as "a woman born to the tribe of Levi," rather than as a biological daughter of Levi himself.8 According to this, Yocheved could still be Amram's aunt, or, alternatively, "דֹּדָתוֹ" could be explained as a relative or cousin.9
"וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה"(Bereshit 15:16) – The Hoil Moshe Bereshit 15:16 explains that "generation" here doesn’t mean a literal generation, but rather the lifespan of an important personality which can extend over several generations.
400 in Bereshit vs. 430 in Shemot – The Hoil Moshe Bereshit 15:16 suggests that 400 is merely used as a round number approximating the more precise tally of 430 years spent in Egypt.10 According to this approach, the prophecy in Bereshit 15 is intended only to be a general foretelling of the future (rather than a precise historical account), and thus both the exact duration and location of the exile are not provided.11
Number of Levites – Shadal and the Hoil Moshe point out that in Shemot 6 only twenty Kehatite descendants are mentioned, while in the second year in the wilderness, Kehat's male descendants numbered 8,600 (see Bemidbar 3:28). As it is impossible that Kehat's descendants multiplied 430 fold in a mere two years, this demonstrates that Shemot 6 cannot be a complete genealogy.12
Israelite population growth – Shadal notes that having a full 430 years in Egypt also more easily explains the nation's growth to 600,000 men. See Fertility Rate for other options.
Biblical genealogies – There are several other instances of characters from the generation of the Exodus whose lineages are traced back to their original tribes but only have a couple of names of ancestors listed in the interim.13 As two or three generations cannot span 430 years, the Hoil Moshe14 suggests that in all of these cases the ancestors named are not the character's father, grandfather, and great-grandfather, but rather his household (בית אב‎), family (משפחה‎) and tribe (שבט‎).15
Duration of the slavery – Theoretically, this approach could posit that the Israelites were enslaved for over 300 years. However, the Hoil Moshe maintains that the harsh decrees spanned only the reign of the two kings mentioned in Sefer Shemot, or a period of about a hundred years.16

Change in Plans

The Israelites were supposed to be in Egypt for a full 400-430 years, but Hashem shortened their stay.

Crux of the position – This approach resolves the discrepancy between four generations and 430/400 years by suggesting that there was a change in the Divine plan. Although Hashem originally decreed a longer exile in Egypt, He later shortened the stay to 210 years.
400 year period – Rabbi Yehuda in the Mekhilta DeRabbi Yishmael notes that the figure of 400 years is inconsistent with the promise of a return of the fourth generation.17 He thus suggests that the verses are presenting two possibilities, a fast track and a slow track. If Avraham's descendants repent, then already the fourth generation will be redeemed, but if not, there will be a full 400 years.18 Similarly, the Pesikta and Tanchuma say that Hashem hastened the redemption by shortening the 400 year decree to 210 years.19
Hashem changing his mind – Tanchuma brings this case as a proof for the principle that Hashem sometimes rescinds a negative decree but never retracts a positive decree. See, however, the exact opposite positions of Ramban and Abarbanel below, who suggest that Hashem lengthened the slavery because of the nation's bad deeds. For more, see Change of Heart.
430 year period – The Midrashic motif of Hashem hastening the redemption would appear to be applicable only to the 400 year prophecy and not to the 430 figure which is part of an after the fact summation.20 However, Pirkei DeRabbi Eliezer attempts to apply it to the 430 number as well. He suggests that Hashem doubled the 215 years spent in Egypt21 by counting both the days and nights, thus arriving at the 430 year total.
Only 210 years in Egypt – According to Rabbi Yehuda in the Mekhilta DeRabbi Yishmael, Hashem could have shortened the 400 year period by any amount, and there is no evidence for specifically a 210 year stint.22 However, the Pesikta and Tanchuma specify that Hashem reduced the decree to 210 years. They are likely influenced by the position of Seder Olam Rabbah below.23
Israelite population growth – The Mekhilta DeRabbi Yishmael,24 Pesikta,25 and Tanchuma26 all explain that the growth was supernatural. See Fertility Rate for more.

Never 430 Years

The Israelites were never supposed to be in Egypt for a full 400-430 years, and the verses which speak of a 400 or 430 year stay need to be reinterpreted as counting, not from the descent to Egypt, but rather from a different starting point.27 This option subdivides regarding the point from which the 430 years are counted:28

430 Years From Avraham's Aliyah

The 430 years are counted from the time when Avraham began his journey to the land of Israel. There are two variations of this possibility:

Departure at Age 70

The 430 year count begins when Avraham originally departed Ur Kasdim at the age of 70.29

Crux of the position – This approach suggests that the 430 year count begins when Avraham departed Ur Kasdim at the age of 70 while the 400 years is counted from the birth of Yitzchak (the beginning of the sojourn of Avraham's "seed"). The exile in Egypt, then, lasted 210 years.
Only 210 years in Egypt – According to these commentators, 220 of the 430 years preceded the descent to Egypt,32 and the Israelites were in Egypt itself for less than half of the 430 total. R. Saadia and others explain that the maximum total of the years listed in the genealogy of Shemot 6 leaves no choice other than to say that the 430 includes years spent outside of Egypt. However, the exact figure of 210 years, although widely known, is not based on any explicit Biblical text.33
430 year period – "וּמוֹשַׁב בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם שְׁלֹשִׁים שָׁנָה וְאַרְבַּע מֵאוֹת שָׁנָה" (Shemot 12:40) – This verse can be reconciled with the above approach in three different ways:
  • Reinterpreting two of its terms – R. Saadia adopts this method. Thus he suggests that "בְּנֵי יִשְׂרָאֵל" can refer also to the Israelites' ancestors such as Avraham,34 and that "בְּמִצְרָיִם" encompasses not only Egypt proper, but all lands which were under Egyptian dominion.35 These broader definitions then allow him to explain that the 430 figure includes also the years from the time that the Patriarchs lived in Canaan and Charan (as those lands were then under Egyptian control).36
  • Assuming that the verse is giving only the central facts and not the full details – R. Yosef Bekhor Shor thus explains that the verse mentions only the stay in Egypt because that was the main part of the exile.37
  • Separating the 430 figure from the rest of the verse – R. Avraham b. HaRambam suggests that the verse is merely saying that the Israelites were in Egypt until the end of the 430 year Patriarchal era which began with Avraham.38
400 year period – "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם וַעֲבָדוּם וְעִנּוּ אֹתָם אַרְבַּע מֵאוֹת שָׁנָה" (Bereshit 15:13) – R. Saadia explains that 400 years is the sum total for all of the events described in the verse (including "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם"), and does not refer exclusively to the slavery itself ("וַעֲבָדוּם וְעִנּוּ אֹתָם")‎.39 In addition, this approach needs to maintain that "בְּאֶרֶץ לֹא לָהֶם" includes Canaan.40
430 in Shemot vs. 400 in Bereshit – R. Saadia explains that while the 430 years in Shemot 12:40-41 start with Avraham's own journey, the 400 years in Bereshit 15:13 begin only with the birth of Yitzchak thirty years later, as this verse specifies "זַרְעֲךָ".
Additional unsubstantiated assumptions – For this approach to be viable, it must assume that Avraham was 70 years old when he left Ur Kasdim (together with Terach).41 R. Saadia notes, however, that this age is not explicit in the Biblical text.42
"וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה"(Bereshit 15:16) and Biblical genealogies – According to this approach, the Israelites were in Egypt for only 210 years, a period short enough to be covered by four generations. Similarly, the lineages of Moshe and other characters in the Torah are complete and do not omit any generations, and the fourth generation in fact returned to the land of Israel.43 Moshe's maternal lineage, however, poses a greater challenge – see discussion below of Seder Olam Rabbah's position.
Duration of the slavery – As Shemot 1:6 implies that the entire generation of Yosef and his brothers died before the oppression began, we must deduct the 94 years Levi lived in Egypt from the 210 year total. This leaves a maximum of 116 years of slavery.44
Arrival at Age 75

The 430 year count begins when Avraham arrived in the land of Canaan at age 75.45

Crux of the position – Demetrius and Josephus propose that the 430 year count begins when Avraham arrived in the land of Canaan at age 75, and they apparently view the 400 as merely a round number. The nation was thus in Egypt for a total of 215 years.
215 years in Egypt – According to this position, 215 of the 430 years transpired before the descent to Egypt,48 and the Israelites were in Egypt itself for exactly half of the 430 years.49
430 year period – "וּמוֹשַׁב בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם שְׁלֹשִׁים שָׁנָה וְאַרְבַּע מֵאוֹת שָׁנָה" (Shemot 12:40) – Demetrius and Josephus utilized the text of the Septuagint which reads "in the land, Egypt, and in the land of Chanaan."50 The version of the LXX they were using may also have read "they and their fathers" like Codex Alexandrinus.51
400 year period – "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם וַעֲבָדוּם וְעִנּוּ אֹתָם אַרְבַּע מֵאוֹת שָׁנָה" (Bereshit 15:13) – According to this position, the 400 figure is an approximation52 of the 405 years Avraham's descendants sojourned in Canaan and Egypt before the Exodus.53
430 in Shemot vs. 400 in Bereshit – The 430 years include Avraham's own years in Canaan, while the 400 figure is a round number which approximates the 405 years from the birth of Yitzchak (as this verse specifies "זַרְעֲךָ").
"וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה"(Bereshit 15:16) and Biblical genealogies – The 215 years in Egypt is a period short enough to be covered by four generations, and Demetrius provides a reconstructed chronology of Moshe's ancestors.54 Demetrius55 also presents Yocheved as Amram's cousin, rather than aunt. Inserting an extra generation between Yocheved and Levi significantly reduces their requisite average age at childbirth, and thus obviates the chronological difficulty presented by Moshe's maternal lineage.

430 Years From Covenant

The 430 years are counted from the Covenant of the Pieces (ברית בין הבתרים). This possibility further subdivides regarding when the Covenant took place:

Covenant at Age 70

The Covenant of the Pieces (ברית בין הבתרים) occurred when Avraham was 70 years old.56

Crux of the position – This approach suggests that the 430 years began with the Covenant which happened when Avraham was 70 years old. It thus needs to rearrange the chronology of Sefer Bereshit and also assume either that the Covenant took place outside of Israel or that Avraham came to Israel only to leave and return again. The 400 years are counted from the birth of Yitzchak. This leaves 210 years for the sojourn in Egypt.
Only 210 years in Egypt – According to this position, 220 of the 430 years preceded the descent to Egypt,58 and the Israelites were in Egypt itself for less than half of the 430 total. Seder Olam and the Mekhilta DeRashbi explain that the maximum total of the years listed in the genealogy of Shemot 6 leaves no option but to say that the 430 includes years spent outside of Egypt. However, the exact figure of 210 years, although widely known, is not based on any explicit Biblical text.59
430 year period – "וּמוֹשַׁב בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם שְׁלֹשִׁים שָׁנָה וְאַרְבַּע מֵאוֹת שָׁנָה" (Shemot 12:40) – The sources taking this position can explain this verse in three different ways:60
  • Reinterpreting "בְּנֵי יִשְׂרָאֵל" to refer also to the Israelites' ancestors such as Avraham61 and "בְּמִצְרָיִם" to encompass not only Egypt proper, but all lands which were under Egyptian dominion62 – This appears to be the option adopted by the Mekhilta DeRabbi Yishmael and Mekhilta DeRashbi.
  • Reading the 430 year figure as describing the duration of the Patriarchal period, whose endpoint coincided with the Exodus – R. Shemuel b. Chofni Gaon,63 R. Yonah ibn Janach.64
  • Assuming that the verse is giving only the central facts and not the full details – R. Yosef Bekhor Shor thus explains that the verse mentions only the stay in Egypt because that was the main part of the exile.65
400 year period – "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם וַעֲבָדוּם וְעִנּוּ אֹתָם אַרְבַּע מֵאוֹת שָׁנָה" (Bereshit 15:13) – Seder Olam Rabbah explains that 400 years is the sum total for all of the events described in the verse (including "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם") which began with the birth of Yitzchak, long before the start of the slavery itself ("וַעֲבָדוּם וְעִנּוּ אֹתָם")‎.66 In addition, this approach needs to maintain that "בְּאֶרֶץ לֹא לָהֶם" includes Canaan.67
430 in Shemot vs. 400 in Bereshit – While the 430 years in Shemot 12:40-41 include Avraham himself, the 400 years in Bereshit 15:13 begin only with the birth of Yitzchak thirty years later, as this verse specifies "זַרְעֲךָ".
Additional unsubstantiated assumptions – In order to maintain that the Covenant of the Pieces occurred when Avraham was 70 years old, this approach must make two very far reaching claims:68
  • Achronology – As the events of Bereshit 12-14 and the first part of Bereshit 15 proceed sequentially from when Avraham was 75 years old, the story of the Covenant of the Pieces in Bereshit 15:7-21 cannot be in chronological order and is not a continuation of the first part of Bereshit 15.69
  • Setting – Since according to Bereshit 12:4-5 Avraham arrived in Israel only after he was 75, one must posit either that the Covenant of the Pieces took place outside of Israel before Avraham came to Israel70 or that Avraham had made an earlier pilot trip to Israel before he was 70, left,71 and then returned at 75.72
"וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה"(Bereshit 15:16) and Biblical genealogies – According to this approach, four generations would suffice to cover the 210 years, and the lineages of Moshe and other characters in the Torah are complete and do not omit any generations.73 Moshe's maternal lineage, however, is more difficult, especially according to Seder Olam Rabbah 9 which says that Yocheved was already alive when Yaakov's family arrived in Egypt.74 This would make her 130 years old when she gave birth to Moshe, 80 years before the Exodus.75 Alternatively, Yocheved could have been born at some point after the Israelites arrived in Egypt. Either way, though, the sum of Levi's and Yocheved's ages at childbirth must total 173.76
Duration of the slavery – Seder Olam Rabbah derives from Shemot 1:6 that the entire generation of Yosef and his brothers died before the Israelites were enslaved. It thus deducts the 94 years Levi lived in Egypt from the 210 year total and gives 116 as the maximum number of years of slavery. It also says that the slavery lasted no less than the 86/87 year age of Miryam at the Exodus.77
Israelite population growth – The Mekhilta DeRabbi Yishmael78 and Rashi Shemot 1:7 explain that the growth was supernatural. See Fertility Rate for more.
Covenant at Age 80

The Covenant of the Pieces (ברית בין הבתרים) occurred when Avraham was 80 years old.

Crux of the position – Ramban suggests that the 430 years began with the Covenant which occurred when Avraham was 80, midway between the ages mentioned in the surrounding chapters. This leaves 220 years for the actual sojourn in Egypt. To reconcile the discrepancy between 400 and 430, Ramban suggests that the original plan included 400 years of wandering but an additional 30 were added later due to the sins of the nation.
220 years in Egypt – The Torah does not give us Avraham's age at the time of the Covenant of Pieces, and thus Ramban estimates it at ~80, or midway between Avraham's recorded ages of 75 and 85-86 in the neighboring chapters.80 According to this, 210 of the 430 years preceded the descent to Egypt,81 leaving 220 years for the stay in Egypt.82
430 year period – "וּמוֹשַׁב בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם שְׁלֹשִׁים שָׁנָה וְאַרְבַּע מֵאוֹת שָׁנָה" (Shemot 12:40) – Ramban offers two possible understandings of this verse in two different works:
  • In his Commentary on the Torah, Ramban suggests that the verse is an elliptical construction and should be read as if the word "עַד" precedes the 430 years. Thus, he interprets the 430 as referring to the aforementioned period specified to Avraham at the Covenant of the Pieces,83 rather than to the time spent in Egypt.84
  • In his Critique of the Rambam's Sefer HaMitzvot, Ramban posits that the verse is speaking generally about the majority of the 430 years, which was in fact spent in Egypt.85 Ramban also adds that the 430 year period began with Avraham's first exile from Canaan. Assuming that Ramban is referring to Avraham's descent to Egypt,86 the 430 years would then be bookended by two exiles to Egypt.
400 year period – "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם וַעֲבָדוּם וְעִנּוּ אֹתָם אַרְבַּע מֵאוֹת שָׁנָה" (Bereshit 15:13) – Ramban is forced to make several assumptions in attempting to read this verse according to his approach:
  • Ramban explains that the verse is a מקרא מסורס and "אַרְבַּע מֵאוֹת שָׁנָה" is a dangling modifier which refers back to "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם", rather than to the immediately preceding words of "וַעֲבָדוּם וְעִנּוּ אֹתָם"‎.87
  • Ramban maintains that the 400 years incorporate the years of Avraham himself from the time of the Covenant,88 in spite of the fact that the verse specifies "זַרְעֲךָ"‎.89
  • Ramban must argue that "בְּאֶרֶץ לֹא לָהֶם" includes Canaan.90
430 in Shemot vs. 400 in Bereshit – Ramban presents two possible ways of reconciling the two numbers:
  • The verses in Bereshit should be understood as saying that following the 400 years, there will be an additional period of thirty years until the Amorites are fully deserving of punishment and the Israelites will return to the land.
  • The verse in Bereshit describes the original plan which called for only 400 years of wandering and oppression. Ultimately, however, their exile was prolonged by thirty years as a penalty for bad behavior,91 and thus Shemot speaks of 430 years.92
"וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה"(Bereshit 15:16) and Biblical genealogies – Ramban Bereshit 15:16 explains that the fourth generation refers to the Amorites.93 In his commentary to Bereshit 46:15 he dismisses the difficulty arising from the advanced age at which children are born to Levi and/or Yocheved, noting that Tanakh is replete with miracles94 and that nature was different at that time.95
Covenant at Age 85

The Covenant of the Pieces (ברית בין הבתרים) occurred when Avraham was 85 years old.

Crux of the position – According to Ralbag, the 430 years began with the Covenant of the Pieces which took place when Avraham was 85 years old, the age recorded in the very next chapter. The 400 years begin from the birth of Yaakov. In order to reconcile this number with the 430 which began 75 years earlier, Ralbag must suggest that Hashem decided to shorten this original decree by 45 years, leaving 225 years for the Egyptian exile.
225 years in Egypt – Ralbag assumes that Avraham was 85 at the time of the Covenant of Pieces,97 as this is his age in the following chapter.98 According to this, 205 of the 430 years preceded the descent to Egypt,99 leaving 225 years for the stay in Egypt.
430 year period – "וּמוֹשַׁב בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם שְׁלֹשִׁים שָׁנָה וְאַרְבַּע מֵאוֹת שָׁנָה" (Shemot 12:40) – Ralbag interprets like Ramban100 that the verse is an elliptical construction and should be read as if the word "עַד" precedes the 430 years. Thus, the 430 years refer to the period specified to Avraham at the Covenant of the Pieces, rather than to the time actually spent in Egypt.
400 year period – "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם וַעֲבָדוּם וְעִנּוּ אֹתָם אַרְבַּע מֵאוֹת שָׁנָה" (Bereshit 15:13) – Ralbag makes three assumptions in explaining this verse:
  • Ralbag says that "זַרְעֲךָ" refers to Yaakov and the 400 years are counted from his birth, as Yaakov spent much of his life wandering and was the first to dwell in Egypt on a permanent basis.101
  • Ralbag suggests that this verse is also slightly elliptical, and is saying that the bondage will last until the end of the 400 year period which began with the birth of Yaakov.102
  • Ralbag says that ultimately Hashem shortened the 400 year decree by 45 years.103 This allows him to reconcile it with the 430 count which began 75 years earlier.104
430 in Shemot vs. 400 in Bereshit – Ralbag does not explain why the 400 years begins only with the birth of Yaakov, while the 430 years starts already at the Covenant of the Pieces.105
"וְדוֹר רְבִיעִי יָשׁוּבוּ הֵנָּה"(Bereshit 15:16) and Biblical genealogies – Ralbag Shemot 2:1 suggests that Yocheved was born at the very end of Levi's life, which according to him was 87 years after the descent to Egypt106 and 138 years before the Exodus. This would make Yocheved only 58 when she gave birth to Moshe.

430 Years From Yitzchak's Birth

The 430 years are counted from the birth of Yitzchak, when Avraham was 100 years old.

Crux of the position – This approach counts the 430 years from the birth of Yitzchak, according to which the actual stay in Egypt was 240 years. Abarbanel explains that the 400 years is either a round number or, like Ramban above, that 30 years were later added due to the nation's sins.
240 years in Egypt – As Yitzchak was born 190 years before the descent to Egypt,109 240 years remain for the actual stay in Egypt.
430 year period – "וּמוֹשַׁב בְּנֵי יִשְׂרָאֵל אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם שְׁלֹשִׁים שָׁנָה וְאַרְבַּע מֵאוֹת שָׁנָה" (Shemot 12:40) – Abarbanel reads this verse as if there was an extra word "עִם" preceding "אֲשֶׁר יָשְׁבוּ בְּמִצְרָיִם", meaning that the 430 years is a total for the entire Patriarchal period and not just the time in Egypt.
400 year period – "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם וַעֲבָדוּם וְעִנּוּ אֹתָם אַרְבַּע מֵאוֹת שָׁנָה" (Bereshit 15:13) – Abarbanel explains that the 400 figure is the sum total for all of the events described in the verse (including "גֵר יִהְיֶה זַרְעֲךָ בְּאֶרֶץ לֹא לָהֶם"), and does not refer exclusively to the slavery itself ("וַעֲבָדוּם וְעִנּוּ אֹתָם")‎.110
430 in Shemot vs. 400 in Bereshit – Abarbanel adopts Ramban's theory that the original 400 year decree was extended to 430 years because of the Children of Israel's sins. For the ramifications of this theory, see the links in the discussion of the Ramban above.111 Abarbanel also suggests that the 400 years may simply be a round number.112
Duration of the slavery – According to Jubilees 46, the oppression began after the deaths of Yosef and all of his brothers, and thus lasted 147 years. Abarbanel opts for a lower figure of 86 years for the most severe stage of the oppression (וְעִנּוּ אֹתָם)‎.113