Katha-2-1-3-yena rūpaṃ

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

How is that to be known, other than the knowledge of which Brâhmins do not crave anything. This is explained. By which, i.e., the âtman whose nature is intelligence; all the world clearly knows form, taste, smell, sounds, touches and the pleasurable sensations due to the commingling of the sexes. It may here be objected that the experience of the world is not in the form ‘I know by the âtman distinct from the body, etc.’; but that all the world thinks in the form ‘I, the combination of the body, etc., Know.’ Not so; even the combination of the body, etc., not being distinguishable in its nature from sounds and the rest and being in the nature of a knowable, it is not reasonable to attribute the nature of knower to it; for if the combination of the body, etc., being no other than form, etc., could perceive other forms, etc., even external forms, etc., may perceive their own and

Links
Various resources on the Kathopanishad
Upanishad Series – Katopanishad Commentary by Swami Chinmayananda