Bùkěsīyì 不可思議 (Korean Pulgasaui; Skt. Acintya) — Tang-period Korean (Silla 新羅) monk, disciple of the Esoteric master Śubhakarasiṃha 善無畏 (637–735), and the principal commentator on the second half of the Mahāvairocana-sūtra corpus. Native of the Língmiào-sì 零妙寺 (also written 靈妙寺) in Silla. Travelled to Tang China and became one of Śubhakarasiṃha’s senior disciples in Cháng’ān, alongside 一行 (683–727).
His extant work is the Dà-pílúzhēnà jīng gòngyǎng cìdì-fǎ shū 大毘盧遮那經供養次第法疏 (T39 no. 1797, KR6j0670), a two-fascicle (2卷) sub-commentary on the seventh and final fascicle of the Mahāvairocana-sūtra — that is, the Gòngyǎng cìdì-fǎ 供養次第法 (KR6j0671; T18n0850), which sets out the actual ritual liturgy of abhiṣeka and oblation. Whereas Yīxíng’s Dàrì-jīng shū 大日經疏 (KR6j0662, T1796) covers fascicles 1–6 (the doctrinal-meditative core), the Bùsīyì shū completes the commentarial coverage by treating the ritual fascicle. The work is conventionally dated to the late Kāi-yuán era (730s) on the basis of the catalog ascription and internal references.
He is not otherwise documented; no birth or death dates can be assigned, no other works are securely attributable, and the Sòng Gāosēngzhuàn 宋高僧傳 does not include him. He should not be confused with 杜順 (d. 640) or other masters who carry bùsīyì as an epithet.
Source: DILA Buddhist Person Authority A000094; Fóguāng dàcídiǎn 佛光大辭典 p. 962. For the historical-philological context of his commentary, see Charles D. Orzech, Henrik H. Sørensen, and Richard K. Payne (eds.), Esoteric Buddhism and the Tantras in East Asia (Brill, 2011), the chapters on the Mahāvairocanasūtra commentarial tradition.