Right component supplies the sound:
上 shàng → ràng — a major Old Chinese sound shift that's no longer transparent in modern Mandarin. Note this is the simplified
让; the traditional
讓 had the much more obvious phonetic
襄 xiāng. The 1956 reform substituted
上 to cut strokes, sacrificing phonetic transparency for writing speed. The 'up' meaning of
上 plays no role.
