At times, achronology in the text is a result of technical literary issues. In many cases, the majority and core of a given story is recorded in its proper chronological place and it is just one or two secondary components which are displaced. The displaced unit might be moved from elsewhere to join and thereby complete the central story ("להשלים את הענין") or it might be separated from the main narrative so as not to interrupt the story line ("לא להפסיק את הענין").
Preludes and Epilogues: "להשלים את הענין"
A subordinate component of a story might be moved from its proper chronological place so as to complete a central narrative. It can take the form of a prelude before the main story or an epilogue at the end.
Prelude
An event which occurred earlier is displaced to serve as an introduction and provide necessary background to a later story.
Birth of Kayin and Hevel (Bereshit 4:1) – According to RashiBereshit 4:1Yeshayahu 1:1About R. Shelomo Yitzchaki, the birth of Kayin and Hevel took place already in the Garden of Eden, before the expulsion.1 It is mentioned afterwards, in Chapter 4, only because it is necessary to open the Kayin and Hevel story.
Sarah conceives (Bereshit 21:1) – According to several commentators,2 Sarah had conceived before or in the middle of the story of Avimelekh described in Bereshit 20.3 The fact is recorded here, though, so as to introduce the story of Yitzchak's birth and weaning.
Marriage of Amram and Yocheved (Shemot 2:1) – R"Y Bekhor ShorShemot 2:1About R. Yosef Bekhor Shor maintains that Amram and Yocheved had married before the decree of Paroh discussed in Shemot 1.4 Their marriage is mentioned later so as to properly open the story of Moshe's birth and its aftermath.
Pesach (Bemidbar 9) – AbarbanelBemidbar 9About R. Yitzchak Abarbanel suggests that the story of the impure who could not participate in the Pesach of the first year is mentioned in the beginning of Bemidbar 9, not because it occurred there, but only to serve as a prelude to the main story of the unit, Pesach Sheni.5 Without the background of the events of the first month, the request of the impure would not make sense to the reader.
Shemuel's death (Shemuel I 28:3) – The death of Shemuel is mentioned in the beginning of the story of the Ba'alat Ha'Ov even though it occurred back in Shemuel I 25, as it provides important background to understand the story's continuation and revival of the prophet.
Epilogue
A component of a story which is only to occur later is moved earlier to provide closure to the main unit.
Death notices – The deaths of the various characters in Sefer Bereshit are recorded already when they fade from the scene,6 rather then in the middle of later narratives when they chronologically occurred.7 The achronology is motivated by a desire to provide closure to each protagonist's individual story.8
The manna (Shemot 16:32-35) – Shemot 16 tells the story of the manna's initial arrival in the first year in the Wilderness, but it also mentions its later preservation near the Ark9 and its being eaten throughout the forty years of wandering. Despite the fact that these added details occur only later, they are placed here to close the unit.10 [For a spectrum of opinions regarding the specific timing of the events mentioned in the epilogue, see Epilogue to the Manna Story.]
Recording the battle of Amalek (Shemot 17:14) – After the battle of Amalek, Hashem tells Moshe to record the event for posterity in "the book" and to speak to Yehoshua about wiping out Amalek. Ibn EzraShemot Short Commentary 17:14About R. Avraham ibn Ezra posits that this was first commanded in the fortieth year.11 In order to finish the story, however, the directive is recorded here.
Yitro's departure (Shemot 18:27) – ShadalBereshit 11:32Bemidbar 8:7Bemidbar 20:1About R. Shemuel David Luzzatto12 posits that the story of Yitro's arrival, advice, and its implementation all occurred where found, in Shemot 18 before the Revelation at Sinai, but that Yitro's departure took place only later. Though Yitro first left in the second year, the fact is recorded already in Shemot to "complete the story".13 [See Chronology – Shemot 18 for elaboration and for those who maintain that other parts of the story, too, might only be mentioned here to "finish the narrative".]
Incense altar (Shemot 30:1-10) – See the discussion in Purpose and Placement of the Incense Altar14 for the possibility that the directive to build the Mishkan preceded the Sin of the Golden Calf, but that the Incense Altar was commanded only in its aftermath. If so, the proper placement of the command should be after the sin in Shemot 34, but it is mentioned earlier to close the unit on the vessels of the Mishkan.15
Erecting the Tabernacle (Shemot 40) – According to those who maintain that the Days of Consecration of the Mishkan (described in Vayikra 8-9) began on the 23rd of Adar,16 the description of the erection of the Mishkan on the first of Nissan (described in Shemot 40) is out of place. One might suggest that it is mentioned here only to serve as an epilogue to the unit of chapters discussing the building of the Mishkan.17
Clouds on the Mishkan (Shemot 40:36-38) – After discussing the erection of the Tabernacle in Shemot 40, the final verses of the chapter speak of the role to be played by the cloud as an indicator of when to travel, adding that this was a constant throughout their journeys in the Wilderness (ie. throughout the forty years). Though this refers to what is to occur in the future, it is mentioned here as a conclusion to the discussion of the cloud of glory which descended on the Mishkan when it was constructed.
Conquest of Canaanite cities (Bemidbar 21:3) – RambanBemidbar 21:1About R. Moshe b. Nachman suggests that the conquest of the Canaanite cities mentioned here occurred first in Shofetim 1:16-17. It is mentioned already here, though, to complete the story, telling the reader how the nation's vow was fulfilled..
Summary
An episode which occurred and was explicitly mentioned earlier in Tanakh is repeated in order to serve as a summary to a unit.
Headings
An event which is soon to be discussed in the text is mentioned already in the heading of the unit, letting the reader know what is to come. This might take the form of a "כלל ופרט", a general formulation followed by details.
Prologues and Appendices: "לא להפסיק את הענין"
Secondary narrative components might be moved to form a prologue at the very beginning of a unit or an appendix at the end because setting them in their proper chronological place in the middle of the central unit would otherwise break the flow of the main narrative . The episode or topic which is displaced is either irrelevant to the main theme or message of the unit, of lesser import, or of a different literary character.
Prologues
An event is moved from its correct chronological place later in the text and placed at the very beginning of the unit where it will not disrupt the main topic.
Bemidbar 1-6 – Though the opening census or Sefer Bemidbar is dated to the second month (Bemidbar 1:1-3), and really occurs in between the events of Chapters 9 and 10, placing such an extensive list of numbers there would break up the main narrative of the book. As such, the Torah might have preferred to incorporate the non-narrative material of Chapters 1-6 as a prologue to the book where it would not interrupt the stories of the Wilderness journey.
Appendices
An episode is moved from its correct chronological place earlier in the narrative and placed at the very end of the unit where it will not disrupt the main topic.
Marriage to Keturah (Bereshit 25:1-6) – According to ShadalBereshit 11:32Shemot 18:1Bemidbar 8:7Bemidbar 20:1About R. Shemuel David Luzzatto, Avraham's marriage to Keturah occurred before Sarah's death and not where it is found. Since the story is tangential to the main narrative which focuses on the formation of the Nation of Israel, it is put as an appendix to the Avraham stories rather than in its proper chronological place. [For elaboration and dissenting opinions, see Avraham's Many Wives]
Genealogy lists (Bereshit 25, 36) – The genealogies of Yishmael and Esav are listed as appendices to the Avraham and Yitzchak stories respectively.18 Even though some of their descendants were likely born during the lives of their grandparents,19 the list is mentioned only at the end of the entire cycle of stories so as not to interrupt the main narrative which focuses on the chosen rather than rejected lines.
Moshe's Blessings (Devarim 33) – Ibn EzraDevarim 31:1About R. Avraham ibn Ezra suggests that Moshe's final blessings to the nation were given over beforehand, in Devarim 31, when he went to encourage the nation and Yehoshua. Due to the unique poetic character of the speech which would be intrusive in place, they are pushed to the end of the book.
End of Sefer Shofetim – Several commentators20 assume that the stories of "the idol of Michah" and the "concubine of Givah" discussed in Shofetim 17-21 occurred much earlier in Sefer Shofetim.21 However, as they deviate from the cycle of sin, oppression, return, and salvation that marks the rest of the book, they are set apart and recorded only at the end
End of Sefer Shemuel – The composition of David's song of Shemuel I 22 and the feats of David's warriors listed in Shemuel II 23 likely occurred at various points earlier in David's career,22 but are grouped as appendices at the end of the book. Here, too, this might be due to the unique nature of the material (poetry / list) and different focus (David's men rather than David) which set them apart from the narrative of the rest of the book.
Miscellaneous
Thematic Arrangement: Parallel Units
Tanakh will often prefer thematic ordering over strict chronology, juxtaposing related material even if this means not adhering to a historical timeline. This is perhaps most evident when components of two independent stories overlap in time. Tanakh will focus on each story individually rather than constantly switching back and forth between the two. As such, the same overall time period might be discussed from different vantage points, with material grouped by varying protagonists, perspectives, literary genre or other factors.
Figures
Tanakh will often focus on one individual protagonist at a time, even if this means compromising on chronological order.
Births of Yaakov's Children – A simple reading of Bereshit 29-30 might imply that Yaakov's twelve children were born consecutively. Yet as this would seem to leave just a little over 6 years for the births of all 12 children,23 several commentators suggest that some of the births must have overlapped.24 Tanakh, though, preferred to separate the stories of each mother, listing each of their births together and only then moving on to the next mother. See opinions in The Births and Relative Ages of Yaakov's Children for elaboration and other approaches.
Yehuda vs. Yosef – The personal story of Yehuda's marriage and children (Bereshit 38) takes place over many years and parts of it likely overlapped with the stories of both Yosef's sale (Bereshit 37) and Yosef's stay in Egypt (Bereshit 39ff).25 Tanakh, though, separates the narratives of the two figures, placing the entire Yehuda tale together so as not to have to constantly interweave the two story lines.26 [See The Births and Relative Ages of Yaakov's Children and Purpose of the Yehuda and Tamar Story for more.]
Preparation for revelation (Shemot 19 and 24) – According to RashiShemot 19:11About R. Shelomo Yitzchaki, the story of the covenant and ceremony described in Shemot 24 took place during the three days of preparations discussed in Shemot 19. It is possible that the stories are distinguished because they have distinct foci; while Shemot 19 highlights the role of the nation and laymen, Shemot 24 focuses on the elders.
Bilam and Israel – See Why Was Hashem Angry at Bilam for those who suggest that the interactions between Bilam and Balak in Bemidbar 22-24 take place at the same time as the story of the Sin of Baal Peor in Bemidbar 25. Here, too, the same time period is discussed from two vantage points, one focusing on what was occurring among Israel's enemies and the other on what was happening in the Israelite camp itself.
Yehoshua's Spies – As there would not seem to be enough time for the story of the sending of Yehoshua's spies and their escape to take place between Yehoshua 1 and 3, some have suggested that it overlaps with the events of Chapter 1.27 Tanakh , though, opted for thematic order, first telling of all of Yehoshua's interactions with the nation and then focusing on the two spies.
The Shofetim – The book of Shofetim presents the tenures of each judge as being consecutive, yet there is reason to suggest that they actually overlapped28 and that parts of the book are achronological.29 Here, too, Tanakh prefers thematic order, opting to tell the story of each judge individually.
Shaul and David – Shemuel I 30 and 31 appear to occur simultaneously. David returns to Ziklag and fights the Amalekites at the same time that Shaul and the Israelite army are being defeated by the Philistines on the Mountains of Gilboa. As Tanakh cannot show both events with a split screen and does not want to interweave the two events line by line, it focuses on one protagonist at a time.30
Reigns of the Judean and Israelite kings – The book of Melakhim alternates between the reigns of the kings of Yehuda and Yisrael, focusing on only one kingdom at a time, even though this means that certain elements of each king's reign are told out of order.
Personal vs. National Perspective
When a hero's interactions on the political / national level overlap with what is going on in his personal life, Tanakh will often separate the two strands of the story rather constantly switching back and forth to maintain chronological order.
Banishment of Yishmael – R. Saadia Gaon, R"Y Kara and Rashbam all imply that the story of the covenant with Avimelekh took place after Yitzchak's birth but before or in the middle of the story of Yishmael's banishment.31 Tanakh might have relayed the events achronologically as it preferred to group the episodes that touch on Avraham's personal family life separately from those which relate to his interactions with outsiders.32
Yitzchak Stories – Bereshit 25 tells of Yitzchak marriage, the birth of Yaakov and Esav, and their upbringing. These events likely overlapped with those of Bereshit 26, with the first half of Bereshit 26 (the wife-sister story) occurring before the birth (for otherwise it is very difficult to understand how Avimelekh did not know of Rivka and Yitzchak's marital status) and the second half (the covenant) taking place later on. Rather than interweaving the various elements of each story as a strict chronology would dictate, Torah separates the personal and political strands of the Yitzchak narrative.
Yosef in Egypt – After narrating the story of Yosef's interactions with his brothers in Bereshit 42-46, Chapter 47 speaks of how the Egyptians themselves fared throughout the famine. If Bereshit 47:18's mention of the "שָּׁנָה הַשֵּׁנִית" refers to the second year of the famine33 (rather than two years after the family's arrival in Egypt), then the events of the chapter overlap with those of the previous ones. Here, too Torah portrays the same time period from two perspectives, first focusing on Yosef and his family and then on Yosef and the Egyptians.
Shaul meeting David – See Chronology of Shemuel I 16 – 17 for an approach which suggests that the search for a musician described in Shemuel I 16 took place during the war with the Philistines described in Chapter 17.34 Once again, Tanakh tells the story from two different perspectives in the textual equivalent of a split screen. Chapter 16 focuses on events relating to the personal life of Shaul, while Chapter 17 focuses on those that relate to Israel at large.
David and Batsheva – The story of David's sin with Batsheva and its aftermath spans Shemuel II 11-12, and takes place over at least two years. This likely overlapped with the end of the ward against Ammon described in 12:26-31, yet the two events are told as independent stories with Tanakh focusing on the personal and national spheres separately.
Individual vs. Universal
Torah might prefer to separate discussions that are of universal import from those which focus on the individual.
Two Stories of Creation – The achronology found in the two accounts of Creation can be explained by positing that Tanakh is telling the same event from two perspectives, starting with the universal and then narrowing in to focus on the creation of Adam. For further discussion, see Two Accounts of Creation.
Law vs. Narrative
Torah tends to separate its discussion of legal and narrative material. Thus, even if a unit of laws was relayed over a period of time and other events occurred simultaneously, Torah will distinguish between the two.
YItro'a arrival – Rashbam posits that all of Chapter 18 (Yitro's arival. advice and its implementation) occured after receiving the Decalogue but before the construction of the Tabernacle. It is placed earlier in order not to break up the continuity of the legal section which follows with an unrelated narrative.