A type of Hetvābhāsa (fallacy (pseudo-probans));
the Hetu (statement of Sādhana (proban or minor term)), the nature of which cannot be trusted due to the lack of proof, doubt or error, e.g., sound is perishable, since it is visible.
apratīyamānasvarūpo'siddhaḥ.
yasya hetorajñānāt sandehād, viparyayād vā svarūpaṃ na pratīyate sa asiddhaḥ, yathā- anityaḥ śabdaḥ, cākṣuṣatvāt.
(Bhikṣu 3.17 Vṛ)