This paper is a research of the arguments on the substantiality of prāpti between Vasubandhu and Saṃghabhadra. The prāpti is a philosophical topic in Sarvāstivādin which has been criticized in Abhidharmakośa by Vasubandhu. In ‘the chapter of the organs’(indriya-nirdeśa), Vasubandhu, at first, has presented the general definition of prāpti. According to him, Sarvāstivādin regard the prāpti as a substance(dravya) because of its effects of ‘the arising cause(utpattihetu) of dharmas’ and ‘the determinant cause of [beings’] state’(vyavasthāhetu). Secondly, He has pointed out the contradiction of the concept of prāpti as a substance itself and has denied its substantiality. Finally, he has presented the new expression, that is to say ‘seed’(bīja) which replace the prāpti. ‘Seed’ is an metaphorical expression which significate the complex of five skandhas, capable of produce the fruit either immediately or gradually in the process of the evolution(pariṇāviśeṣa) of the series(saṃtati). It is not a substance but dharma as a designation(prajñapti-dharma) which indicate the state(avasthā) of a person(āśraya). Against Vasubandhu, Saṃghabhadra firstly redefine the effects of prāpti. For him, prāpti is undoubtedly a substance because it is ‘the keeping cause(avipraṇāśa-kāraṇa) of dharmas’ and ‘the sign of distinction’(jñāna-cihna) which is inclusive of ‘the determinant cause of [beings’] state’(vyavasthāhetu) presented by Vasubandu in Abhidharmakośa. Secondly, By reexaminating so-called ‘the Doctrine of Seed’ he has logically deconstructed the notion of ‘seed’ and pointed out the contradiction of the expressions which indicate the states of ‘seed’, for example ‘perfect destruction of seed’, ‘possession of seed’. For him, ‘Seed’ is an absurd notion in logic because of the ambiguity that the seed of an dharma is not simultaneous nor successive with the dharma. Especially, the expression ‘imperfect destruction’ of good dharma or passion’s seed’ has been presented as a typical example of its ambiguity. Because he cannot accept the third state between destruction and possession. Finally, After negation of ‘seed’, he has reconstructed the prāpti as a substance. The arguments on prāpti and bīja between Vasubandhu and Saṃghabhadra seem to me a moment of exposing the differences in their ontological positions. Firstly, Vasubandhu cannot accept the substantiality of prāpti in Sarvāstivādin. Their notion of prāpti implicate a kind of essentialist preposition that there is a intrinsic difference between saint(ārya) and mediocrity(pṛthagjana) as we can clearly see from ‘the determinant cause of [beings’] state’(vyavasthāhetu). Secondly, Saṃghabhadra, on the contrary, cannot accept the ambiguity of Vasubadhu s bīja. According to so-called ‘The Doctrine of Being as Substance of Dharmas in All Three Moments’ in Sarvāstivādin, a dharma has a same essence(svabhāva) either in a former or later moment(kṣaṇa). Accordingly, ‘the Doctirne of Seed’ that can approve a borderline concept, i.e. ‘seed’ between dharmas in a former and later moments seems to him a danger that may deny the identity between the former and the latter. In conclusion, while the position of Vasubandhu as ‘a master of Sautrāntika’(Sūtrakāra) is relatively nominalistic, Saṃghabhadra as a master of Sarvāstivādin is more realistic, close to essentialist philosophy.