By strict definition, a replacement child is one who is conceived because an older sibling has died. According to the theory, such a child is at psychological risk, especially if the dead child has not been adequately mourned.
Because he was an oldest son, Edward Gibbon, the greatest of all modern historians and the most brilliant prose stylist in the English language, would not seem to qualify as a replacement -- except that in his own curious manner of thinking, Gibbon “replaced” children who were born subsequent to him.
Gibbon preened himself on his status in the family. “From my birth,” he said in his famous Memoir, “I have enjoyed the rights of primogeniture.” But primogeniture was not so much a chronological fact as it was a pinnacle to be defended. As he conceived it, Gibbon triumphed over would-be competitors to his supremacy. “I was succeeded by five brothers and one sister, all of whom were snatched away in their infancy.” Toward his dead siblings, and toward the parents who endured the heart-breaking death of six of their seven children, Gibbon was unnaturally cold and mercenary. “I shall not pretend to lament” the loss of those who would “oppress my inheritance.” Gibbon lacked empathy in part because he felt, with some justice, that his younger siblings were favored over him by his father. How could this be?
The Memoir supplies an explanation. In an age of high infant mortality, Gibbon was a very sickly child. His life was at risk while other, later-born children seemed to be healthier. As Gibbon himself puts it, “so feeble was my constitution, so precarious my life, that, in the baptism of each of my brothers my father’s prudence successively repeated my Christian name of Edward, that, in case of the departure of the eldest son, this patronymic appellation might be still perpetuated in the family.” This is odd indeed. In five separate instances, according to the future historian, a male child saw the light, and each time the child was named Edward. In one case after another, the outcome was the same. The infant who might have “oppressed his inheritance” succumbed and the heroic oldest son beat back the challenge. The first Edward therefore “replaced,” so to speak, a series of subsequent Edwards who might have superseded him. It's not hard to imagine that a sickly child, pursued by a series of infants each christened with his very own name, would feel threatened and might rejoice rather than mourn at their funerals.
Although Gibbon attributes the pattern of naming to his father’s “prudence,” it is obvious that the phrase "my father's prudence” is an irony that masks a true fury. Was it prudence or was it his father's hope that the sickly child would be succeeded by an healthy one? Hostility also shines through Gibbon's jealous account of his mother: "to preserve and to rear so frail a being [as himself], the most tender assiduity was scarcely sufficient; and my mother’s attention was somewhat diverted by her frequent pregnancies, by an exclusive passion for her husband, and by the dissipation of the world, in which his taste and authority obliged her to mingle.” The irony of this beautiful Augustan sentence conceals infantine rage: to translate into more forthright English, Gibbon objects that his mother conceived other children, claims that she should have preferred him to her husband, and asserts that she should have withdrawn from society to nurse him.
To what degree Gibbon’s suppressed and ironic but still obvious anger toward his parents contributed to his peculiar temperament is difficult to say, but it is a fact that the bulk of his career was spent not only in tracing the decline and fall of Rome, the father of all European civilizations, but also in displacing an established patriarchal religion from its position of supremacy. The irony that he directed against his parents in his Memoir is the exact weapon that he learned to deploy against Roman failures and against triumphant Christianity.
In addition, there's an untidy psychological wrinkle. Gibbon’s claim that the male children who succeeded him were all named Edward is a crucial part of his indictment of his parents. But it's an assertion that is not true and is not substantiated by parish records. There was no endless series of Edwards. Apparently, one succeeding child was so named but the rest enjoyed various different appellations. The most scrupulous of historians either invented or misremembered the dreadful slight that so wounded him. What psychological mechanism caused Gibbon to yearn to be even more of a replacement child than in fact he was?