Imperial Legitimate Child Succession Code Theory stands on the basis that since after Monmu, the Imperial Throne had been succeeded by imperial legitimate children, and that Ritsuryo (the legal codes of the Nara and Heian Periods) support the legitimate child succession principle.
嫡系皇位継承法説の根拠としては、文武以降の皇位継承が嫡系継承であること、律令が嫡系主義をとっていることが挙げられる。