A four-member family structure consisting of two siblings contrasting in personality (sibling deidentification) and each identified with a different parent (split-parent identification) was recently reported (15). In well-functioning families, this tetrad or quadrangle is widespread in the first pair of siblings in the family and tends to be more common in same-sex pairs, suggesting that sibling deidentification is designed to mitigate the relatively intense sibling rivalry characteristic of these pairs and hence to maintain family harmony.

In this collated case report, deidentification is found to follow the same pattern in 39 clinic first pairs. However, contrasting attributes are varied and nonevaluative in nonclinic pairs but mainly “good-bad” in clinic pairs, with polarization extreme. Results suggest that nonclinic siblings negotiate their identity (being) much as they negotiate about possessions (having) and that negotiations are blocked in clinic pairs, freezing mythic devil or angel identity. Intervention is directed at dislodging this block.