This is thought to be a reform to incorporate the powerful clans, which produced Oomi and Omuraji which were not included in the twelve grades of cap rank system, into the rank system and to establish a rank system with Emperor at the top.
これは従来、冠位十二階に含まれなかった、大臣・大連などを輩出する有力氏族を冠位制度へ組み込み、天皇を頂点とした序列をつける為の改革だと思われる。