# Chronology and interpretation policy

## Biblical sequence and calendar dates are different claims

The biblical text often states that one event occurred before another, that a reign lasted a stated number of years, or that an event followed a feast or earlier event. That is **biblical sequence**. Converting that sequence into a modern BC or AD year may require additional assumptions, synchronisms, textual decisions, and historical evidence.

Bible Timeline must not blur those layers. Scripture references identify the biblical basis. The date label and chronology note explain how confidently the event can be placed on a calendar.

## Date precision and confidence

Every record uses one of these visible precision values:

- `exact`: an event has a strong historical calendar anchor for the resolution claimed. This does not imply that every detail or theological interpretation is externally verified.
- `approximate`: the displayed calendar date or range is a reconstruction and remains visibly qualified.
- `disputed`: meaningful alternative placements exist or the available evidence does not support one unqualified date.
- `sequence-only`: the relative order or interval is supplied by Scripture, while an exact calendar date is not asserted.

Precision is separate from `high`, `moderate`, or `low` chronology confidence and a required explanatory note. The interface shows these distinctions in words, border patterns, and badges and does not rely on color alone.

## Approximate and disputed dating

Use “approximately,” “commonly estimated,” `c.`, a range, or named alternatives in `displayDate` when the evidence calls for qualification. Do not convert an internal sorting value into an unqualified public claim.

For the Exodus, this milestone names the broad 15th- and 13th-century BC proposals rather than selecting one. Similar contested issues should remain visible until the project supports documented alternative chronology views.

## No year zero

The user-facing chronology uses BC and AD. In that convention, 1 BC is followed by AD 1; there is no year zero. Internal signed years therefore use negative integers for BC and positive integers for AD, and validation rejects zero. For proportional layout only, the shared core converts them to a continuous ordinal in which 1 BC is immediately followed by AD 1.

Internal numeric years exist to sort and position records. The readable chronology `display` value remains authoritative for presentation and may contain ranges or uncertainty that a single number cannot express.

## Creation and the selected traditional comparison model

Biblical History uses a **c. 4004 BC traditional/Ussher-style visual anchor** so its opening span reflects the project’s selected traditional model. This is a calculated comparison position, not a modern BC date explicitly supplied by Genesis and not a statement of scholarly or theological consensus. The event remains `sequence-only`, with low calendar confidence and high biblical-sequence confidence.

The same separation applies to the displayed c. 2348 BC Flood and c. 2247 BC Babel anchors: Genesis supplies narrative order and internal genealogical notices; the conversion into BC years belongs to a later chronology model. See `chronology-audit.md` for the corrections and sources.

## Future alternative chronologies

The data model stores a sorting anchor, optional end year, qualified visible date, precision, confidence, and chronology note. A later milestone may represent alternatives explicitly as named chronology options with:

- a stable option ID;
- its proposed date or range;
- a concise explanation of its assumptions;
- specific sources;
- a display label that never implies universal agreement.

Readers should eventually be able to compare alternatives without one option silently rewriting the underlying biblical sequence.

## Sources and interpretive transparency

Chronology involves interpretation. The application should cite identifiable sources for reconstructed dates instead of hiding choices behind an authoritative-looking number. A source note must never be fabricated. Records without an attached extra-biblical citation say so without implying that no evidence exists.

As the dataset grows, each historical dating claim should identify the source or chronology used, while Scripture references remain separately labeled. This lets families understand both what the biblical text states and what later historical reasoning contributes.

## Related interpretive layers

Calendar chronology is only one layer. Prophecy fulfillment, Gospel harmonization, and geographic placement have their own uncertainty classifications and notes. They must not inherit certainty merely because a record has a confidently identified Scripture reference. See `prophecy-policy.md`, `gospel-harmony-policy.md`, and `geography-and-maps.md`.