A major goal of the International Institute for Jewish Genealogy and Paul Jacobi Center is to develop research tools and technologies for the use of Jewish genealogists and social scientists generally. One such tool for which there has long been a compelling need is a standard chronological system to record generations on family trees. In addition, genealogy research needs a system that permits the synchronization of generations within kinship groups and their harmonization both with other family trees, whether related or unrelated, and with wider frames of reference, both historical and societal. The Jacobi Absolute Generations Scale (JAGS) provides proven solutions to these various needs.

This article addresses areas that illustrate some of the problems involved both in enumerating the generations using a “relative generations” system and in identifying individuals within them who bear identical names. It then illustrates how the Jacobi Absolute Generations Scale, devised by the late Dr. Paul Jacobi almost half a century ago, fully resolves such problems.

Relative Generations

The simplest way to register generations on a family tree is to define the length of a generation as 25 or 30 years and then to tie the individuals on the tree to a recognized dating system, such as the Gregorian, Hebrew, Julian, or Muslim calendars. Unfortunately, this arbitrary approach is inadequate for researchers for a number of reasons. First, it depends on knowledge of the years of birth and death of individuals on the tree, and these facts often are unknown. As a result, family historians grappling with the problem often adopt a different approach. They choose to designate generations by the number of generations known to them, generally assigning the number 1 to the earliest generation recorded on their particular tree—or their genealogy software program makes this choice for them.

Despite the apparent logic of this system of “relative generations,” it can lead to confusion, inconsistencies, and even errors. One obvious danger may be demonstrated in the case of a family historian who numbers the third generation back (the earliest known to him) as number 1, while another researcher of the same family, who has traced the common lineage further back in time, assigns the number 1 to the fifth or even the fifteenth generation back. The resultant confusion is self-evident.

The potential pitfalls associated with this system, however, run even deeper. Homonymous individuals—multiple individuals with the same name—and married names represent two problem areas.

Homonymous Individuals. Among Ashkenazim, parents customarily name newborn children after close deceased relatives. While several considerations may come into play in selecting given names, a first son often is named after a grandfather or, if the grandfather is still alive, after a great-grandfather. Other children, both male and female, are named in accordance with various conventions, and in some communities, in a well-established (though not iron-clad) order. These customs lead to regular, consistent naming patterns, usually repeating themselves in every third generation and often throughout parallel branches of the same family.

Since family historians frequently use naming patterns as a guiding light to fix generations in time and to determine

Paul Jacobi

re­lationships between individuals, the recurrence of individuals with the same given name (homonymous individual) in a single family lends itself to misidentification and outright mistakes. The problem may be compounded when the same naming pattern is found in another, unrelated family that bears the same surname, sometimes in the same community.

Among Sephardim, especially Ladino-speak­ing Jews, the custom has been (and to an extent still is) to name a child in honor of maternal and paternal grandparents, whether living or dead. Again, the same names may appear many times within a single time frame and not in clearly defined generations, thereby increasing the risk of errors in identity.

    Married Names. In historic Jewish writing, rabbinic writing especially, women tend to be recorded as “so-and-so,” the daughter of “so-and-so” (her father), wife of “so-and-so.” Although in some cases this form of naming may help identification, it frequently leads to confusion, given the multiplicity of the same masculine name in repeated generations within a given family. The problem is compounded by the propensity for cousins to marry cousins in certain Jewish societies.

These factors, homonymous individuals and married names, complicate and hinder comparisons between independently produced family trees, especially when the relative generations system is used for recording purposes. Harmonizing such trees and reconciling inconsistencies between them is far from easy, while the establishment of complex family relationships grows all the more difficult the longer the lineages. Errors are hard to spot and skipped generations may be overlooked, with all the attendant genealogical blunders likely to arise therefrom.

In brief, the relative generations system can become an obstacle to serious genealogical research. Attempts to synchronize the arbitrarily numbered generations with a standard time line may not lead to accurate correlations. Hence, the historical background and cultural context surrounding an individual may be skewed and marred by anachronisms or the opposite. Equally, the influences on his behavior and life choices, his educational and occupational opportunities, residential possibilities, communal affilia­tions and societal networks, and migrational decisions, to mention but a few aspects of life relevant to the genealogist, may be improperly understood.

Absolute Generations

Aware of these difficulties, the late Dr. Paul Jacobi (1911–97) developed an alternative system for registering generations, now known as the Jacobi Absolute Generations Scale (JAGS). In this system, genealogists employ an absolute time line that is stable, recognized, and linked directly to the years enumerated in the system used in the Western world today (e.g., “BC” and “AD” or, for Jews and some others, “BCE” and “CE”).

On the basis of his extensive genealogical knowledge and experience, Jacobi determined the average span of a single generation as 75 years, with each successive generation set to follow the previous one at intervals of 30 years. Thus, on the basis of the Common Era (CE) dating system:

• Generation 1 is fixed as 2040–1965 (a period of 75 years).
• Working backwards, “Generation 2” begins 30 years earlier and covers the period 2010–1935.
• Successive generations are counted retrogressively every 30 years prior to 2010.

With the designation of the current generation as “Generation 0,” Jacobi’s absolute generational scale for the last 900 years can be seen in Table 1. Jacobi drew his scale back to Generation 32 (1035–1110) which corresponds with the life of the great Jewish biblical and Talmudic commentator, Rashi (1040–1105).

Theoretically, Jacobi’s scale could be extended back to the dawn of recorded history, or indeed of history itself, but Jacobi preferred not to be drawn into unnecessary theoretical discussions over when history began and, according to whose historical tradition. As a practical matter, he regarded it as sufficient to use the scale as it is, since scientific Jewish genealogy scarcely predates Rashi.

An individual who lived most of his life within a given generation is designated as belonging to that generation. Thus, the outstanding Jewish scholars, Samuel Eliezer ben Judah Halevi Edels (1555–1631)—the “Maharsha” and Maimonides (1135–1204)—the “Rambam” belong to generations 15 and 29, respectively. Within each absolute generation, the scale allows for flexibility. On occasion, it is necessary—and possible—to split a generation or to skip one. For example:

• A man lived from 1725 to 1755 and had a son who lived from 1744 to 1790. Both belong to Generation 9. For the sake of clarity, however, the father should be assigned to Generation 9b and the son to Generation 9a.
• A woman lived from 1775 to 1830 and had a daughter who lived from 1815 to 1890. The mother belongs to Generation 8, but the daughter to Generation 6—hence the need to skip a generation in this case.

When the need eventually arises, the scale can be extended forward in time by adding Generation–1 (2100–2025), Generation–2 (2130–2055), and so on.

Advantages of Absolute Generations Scale

Several advantages arise from adopting the Jacobi Absolute Generations Scale.

• First and foremost, JAGS offers a standard chronological system to record generations on family trees and to synchronize them within kinship groups.
• Every individual on a specific family tree—and on parallel trees constructed independently—can be assigned to an absolute generation.
• An individual’s generational position is identical on all trees, thereby providing positive identification when trees are compared, merged, or interchanged.
• The JAGS minimizes the possibility of misidentification and of coalescing individuals bearing the same given name and patronym.
• The JAGS readily illustrates anomalies requiring further investigation, such as a married woman whose father was born in generation 12, but whose supposed husband was born 100 years earlier, in generation 15.
• It sometimes suggests solutions to anomalies because facility in using JAGS leads to an ability to place an individual in his correct generation, even in the absence of precise dates of birth and death for the individual concerned.
• JAGS indicates the precise time frame in which a person lived the majority of his life and thereby places him in the correct historical context, even when some vital genealogical information is lacking.
• Assignment of an absolute generation to all family members reveals an individual’s contemporaries, both within his own family and beyond. JAGS permits the reconstruction of generational relationships even when full genealogical information is missing. For example, if an individual can be located in generation 26, one may reasonably assume that his father belonged to generation 27, his children to generation 25 and his grandchildren to generation 24. The subsequent discovery of a critical piece of vital statistical information almost invariably substantiates these assumptions, proving the reliability and value of the scale.
• Use of Jacobi’s Absolute Generations Scale points the way to the creation of a common terminology and chronology between genealogists and researchers from other disciplines, as well as scholars from diverse cultures, speaking different languages.

Use of JAGS

    The Jacobi Absolute Generations Scale is easy to use on commonly employed genealogical software programs, such as Family Tree Maker and Brother’s Keeper. As with other data, such as name, birth and death, an individual’s “absolute generation” must be entered manually, using the following instructions:

    When using Family Tree Maker, to enter an absolute generation observe the following instructions. Open the individual’s “Family View,” click on “Edit,” and then, in the dialogue box, click on “Add Fact.” In the next dialogue box, under “Type,” enter “JAGS,” and under “Place or Description,” enter the number of the individual’s generation, using the scale given above. Click on “OK.” For printouts of “Reports,” or “Tree Charts,” under “Items to Include,” highlight “JAGS” in the “Available Items” box on left and move it to the “Contains” box on right. The JAGS generation number, as entered into the program will then appear in the report or chart. Follow equivalent steps with other software programs.

Dr. Chanan Rapaport was a close collaborator of Paul Jacobi and has tested JAGS over many years. Rapaport lives in Jerusalem and is deputy director of the International Institute for Jewish Genealogy (IIJG). Ambassador Neville Lamdan, director of the IIJG, contributed extensively to this article.