EIGHTEENTH SITUATION, INVOLUNTARY CRIMES OF LOVE

(The Lover; the Beloved ; the Revealer)
This and the following situation stand out as the most fantastic and improbable of all the silhouettes upon our dramatic horizon. Nevertheless they are, in themselves, quite admissible, and at least not rarer today than they were in heroic times, through adultery and prostitution, which never nourished more generally than at present. It is merely the disclosure which is less frequent. Yet many of us have seen certain marriages, apparently suitable, planned and arranged, as it were, by relatives or friends of the families, yet obstinately opposed, avoided and broken off by the parents, seemingly unreasonable, but in reality only too certain of the consanguinity of the lovers. Such revelations, then, still take place, although without their antique and startling eclat, thanks to modern custom and our prudent prudery.
Its reputation for fabulous monstrosity was in reality attached to our Eighteenth Situation by the unequalled celebrity of the theme of "OEdipus," which Sophocles treated in a style almost romantic, and which his imitators have ever since overloaded with fanciful arabesques, more and more chimerical and extraordinary.
This situation and the following—as indeed to some extent all thirty-six—may be represented, as the author chooses, in one of two lights. In the first, the fatal error is revealed, simultaneously to the spectator and to the character, only after it is irreparable, as in Class A; and here the state of mind strongly recalls the Sixteenth. In the second, the spectator, informed of the truth, sees the character walk unconsciously toward the crime, as though in a sinister sort of blindman's-buff, as in Classes B, C and D.
A (1)—Discovery That One Has Married Ones Mother:—the "OEdipus" of Aeschylus, of Sophocles, of Seneca, of Anguillara, of Corneille, of Voltaire, not to speak of those of Achaeus, Philocles, Melitus, Xenocles, Nicomachus, Carcinus, Diogenes, Theodecte, Julius Caesar; nor of those of Jean Prevost, Nicolas de Sainte-Marthe, Lamothe, Ducis, J. Chenier, etc. The greatest praise of Sophocles consists in the astonishment we feel that neither the many imitations, nor the too well-known legend of the abandonment on Cithaeron, nor the old familiar myth of the Sphinx, nor the difference in the ages of the wedded pair,—that none of these things has made his work appear unnatural or unconvincing.
(2)—Discovery That One Has Had a Sister as Mistress:—Tasso's "Torrismond"; "The Bride of Messina" by Schiller. This case, obviously a more frequent one, becomes unconvincing in the latter drama, when combined with the Nineteenth Situation. Example from fiction: "L'Enfant Naturel," by Sue.
B (1)—Discovery That One Has Married Ones Sister:—"Le Manage d' Andre" (Lemaire and de Rouvre, 1882). This being a comedy, the error is discovered in time to De remedied, and the play "ends happily." "Abufar" by Ducis, which also falls under a preceding classification.
(2)—The Same Case, in Which the Crime Has Been Villainously Planned by a Third Person: —"Heraclius" (this gives, despite its genius, rather the feeling of a nightmare than of a terrible re?lity).
(3)—Being Upon the Point of Taking a Sister, Unknowingly, as Mistress:—Ibsen's "Ghosts." The mother, a knowing witness, hesitates to reveal the danger, for fear of subjecting the son to a fatal shock.
C—Being Upon the Point of Violating, Unknowingly, a Daughter:—Partial example: "La Dame aux Domino Rose" (Bouvier, 1882).
D (1)—Being Upon the Point of Committing an Adultery Unknowingly (the only cases I have found in all drama):—"Le Roi Ceff" and "L'Amour des Trois Oranges," both by Gozzi.
(2)—Adultery Committed Unknowingly:—probably the "Alcmene" of Aeschylus; "Le Bon Roi Dagobert" (Rivoire, 1908). From fiction: the end of "The Titan, by Jean-Paul Richter.
The various modifications of incest and other forbidden loves, which will be found in Situation XXVI, may be adapted in the same manner as those here classified.
We have seen above instances of adultery committed through a mistake on the part of the wife; it might also be through a mistake by the husband. This error is especially likely to be made by that one of the two adulterers who is unmarried; what is more common, for example, in the life of "pleasure," than to discover —a little tardily—that ones mistress is a married woman ?
Ignorance of the sex of the beloved is the point upon which "Mademoiselle de Maupin" turns; there is in the first place a mistake (comedy), upon which are built the obsidional struggles of a soul (tragi-comedy), from which there finally results, when the truth is disclosed a brief tragic denouement.
comments
Focuses on the discovery of loving one’s own relative. Example: Oedipus. This one, and #19, says Polti, are the most “fantastic and improbable” situations. The situation can be put forth in one of two ways: (A) the fatal error is revealed simultaneously to the reader and character, only after it is irreparable (as in Oedipus) or (B) the reader knows the truth while the character doesn’t, and watches the character walk into the deed.
Crimes of love are amongst the most socially shocking in the way they break very strong rules against incestuous relationships. The children of incest, of course, can easily be genetically damaged, and hence such relationships are strongly banned in all cultures.
However, when this act is accidental, then a confusing conflict is set up in the viewer, who is both disgusted by the crime and sympathetic to the lover who themselves will be feeling even more internal conflict. The result is a powerful emotional dilemma which pulls on the heart strings and provides a strong story element. 
category:Thirty-Six Dramatic Situations