The Compendium of Caraka 1.11.7_1

1.11.7_1

kasmāt pratyakṣaṃ hyalpam; analpamapratyakṣamasti, yadāgamānumānayuktibhirupalabhyate; yaireva tāvadindiryaiḥ pratyakṣamupalabhyate, tānyeva santi cāpratyakṣāṇi //

Why? For sensory perception is small; vast is the imperceptible, which is grasped through authoritative testimony, inference, and reasoned correlation. Those very sense organs by which the perceptible is grasped are themselves imperceptible.