Ottilie
A circa 1864 depiction of Ottilie and the dead child Otto by German painter Wilhelm von Kaulach (1802-1874). [6]
In Elective Affinities, Ottilie, is the adopted daughter of Charlotte’s deceased best friend, is the fourth of the reactants brought into the estate so to bring about the double elective affinity reaction, as described in Goethe’s affinity table, and is one of the four “Otto” interchangeable chemical species.

Multiple relationships
David Constantine, English translator of the 1994 Oxford World Classics edition of Elective Affinities, likewise argues that Ottilie could have been based on one of three people, firstly Christiane Vulpius, a girl from a local flower shop, who became Goethe’s mistress and whom he lived with for eighteen years. Ottilie could also have been Minna Herzlieb who Goethe began to have feelings for, a year after marrying Christiane; as he comments: [1]

“Goethe wrote a sequence of sonnets for her [Herzlieb]; and it has very often been said that she moved him to write Elective Affinities much as Charlotte Buff had moved him to write Werther, and that she appears in it as Ottilie.”

Constantine, however, also argues that Ottilie could have been Sylvie von Ziegesar whom Goethe was seeing frequently during his usual summer stay in Karlsbad in 1808. It has also been noted that between 1788 and 1816 Goethe was in love, more or less passionately, more or less intimately, half-a-dozen times at least. [1]

Minna Herzlieb
The most-cogent argument for the bulk of the person behind the character Ottilie, however, comes from Goethean scholar Hjalmar Boyesen who, in 1879, explained that Ottilie was based on Minna Herzlieb: [3]

“Goethe’s affair with Minna Herzlieb, the adopted daughter of the bookseller Fromman, in Jena, was a kind of poetic devotion, at a time when he was yet bound to another naturally stimulated him to many reflections concerning the nature and validity of marriage, and these reflections, embodied in living characters, furnished the theme of the novel, Elective Affinities.”

In other words, just as Ottilie was the adopted daughter of Charlotte's deceased best friend, so to was Minna the adopted daughter of one of Goethe's friends, the bookseller Fromman, in Jena, with whom Goethe had developed strong amorous feelings towards. To corroborate, as Goethean historian Calvin Thomas explains: [4]

“[Toward the end of 1807] to while away the otherwise lonely and tedious winter evenings he resorted to the homes of congenial friends, among whom was the bookseller Frommann. One of the members of the Frommann household was Wilhelmina Herzlieb, a shy girl of eighteen year whom Goethe had known casually for ten years. He liked her very much—more than was ‘proper’, as he admitted to Zelter some years later—while she seems to have looked up to him with veneration, counting herself blest to be admitted to such choice society.”

Goethe’s biographer George Lewes points out that “at length it was resolved to send Minna to school, and this absolute separation saved them both” just as “in the novella, Ottilie also is sent back to school.” [2] The main source for the Ottilie character seems to have been Minna Herzlieb.
Person Behind the Character
Christiane Vulpius 75Christiane Vulpius (1765-1816)A girl from a local flower shop, who became Goethe’s mistress (because of her class), whom he lived with for eighteen years; married her in 1806; bore him five children.
Minna Herzlieb 75Minna Herzlieb (1765-1839)In 1807, she came to Weimar, where she met Goethe, who presented her with some sonnets; it has been argued that she may have been one of the models for Ottilie.
Sylvie von Ziegesar 75Sylvie von Ziegesar (1785-1858)Goethe was seeing her frequently during his usual summer stay in Karlsbad in 1808; and it has been said she to was the model for Ottilie. She was the subject of Goethe's poem: "To Sylvie von Ziegesar".
Goethe (1775) 75Johann Goethe (1749-1832)It has been argued that the Ottilie character was based on Goethe's youthful (age 27) entry into the established Charlotte von Stein (age 34) family.

Goethe in youth
One of the more telling suppositions as to the character of Ottilie comes from German philosopher Herman Grimm who argues that the Ottilie character was based on Goethe’s experience in 1776 at the age of 27 when entered the life of Charlotte von Stein (age 34): [5]

“Into their wedded life Ottilie enters, as Goethe once found his way into the Frau von Stein’s family.”

This is corroborated by Goethe’s 1780 writings to Lavater about Frau von Stein:

“She has gradually succeeded to the position of mother, sister, beloved one; and a bond unites us which seems like these natural ties.”

To Goethe, according to Grimm, Stein had become son, brother, lover, all in one. Grimm goes on to allude to the conclusion that the child, or "poor creature" as Grimm calls it, born out of this unnatural relation is Goethe's realization of the disastrous outcome that would have befell him had he stayed with Stein relation in those early years, in that older woman type of situation.

See also
‚óŹ Ottilie Pogwisch

References
1. Constantine, David. (1994). “Introduction” (to English translation of Elective Affinities). Oxford University Press.
2. Lewes, George H. (1864). The Life of Goethe (pg. 504). Smith, Elder and Co.
3. Boyesen, Hjalmar H. (1879). Goethe and Schiller: Their Lives and Collected Works (pgs. 120-24). C. Scribner’s Sons.
4. Thomas, Calvin. (1917). Goethe (pg. 132). H. Holt and Co.
5. Grimm, Herman F. (1880). The Life and Times of Goethe (pg. 465). Trans. Sarah Adams. Little, Brown, and Company.
6. (a) Goethe timeline (elective affinities section)– GoetheZeitPortal.de.
(b) Wilhelm von Kaulbach – Wikipedia.
(c) Ottilie (c.1864) – PDMP Gallery.

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