This study presents a comparative analysis of two concepts concerning the enlargement of the self: self-extension (Belk, 1988) and self-expansion (Aron & Aron, 1986). Based on an extensive review of prior research, this study demonstrates that these concepts differ fundamentally in their motivational aspects, which in turn lead to distinct functions and characteristics. Furthermore, the study reveals that existing measurement scales fail to adequately reflect these conceptual distinctions, pointing to a need for more differentiated and theoretically grounded instruments.