As I discuss in this question, in Hindu philosophy there are three main Pramanas or valid means of knowledge: Pratyaksha or sensory perception, Anumana or inference, and Shabda or scriptural testimony. And there is hierarchy of these Pramanas, as described in verse 6 of Ishwara Krishna's Samkhya Karika:
sāmānyatastu dṛṣṭādatīndriyāṇāṃ pratītiranumānāt ।
tasmādapicāsiddhaṃ paro'kṣamāptāgamāt siddhaṃ ॥
By means of Inference based on Analogy, the objects beyond senses are proved; that which is not proved by this (Inference) and cannot be directly perceived, is proved, by Valid Testimony.
Now the Samkhya Karika Bhashya, attributed to the Advaita philosopher Gaudapada, gives some examples of things which cannot be proven through perception or inference, and thus require scripture to establish:
That which is not proved by this (Inference) and cannot be directly perceived, is proved by Valid Testimony. For example:—Indra, the king of gods; the northern Kurus; the nymphs in the Heaven;—all these imperceptibles are proved by Valid Testimony.
Now it's understandable that the existence of Indra and the Apsaras of Swarga cannot be proven through perception or inference. But my question is, why does Gaudapada say that the existence of the Uttarakurus, who live on the other side of the Himalayas, cannot be proven through perception or inference.
This is of a piece with a bunch of strange statements that Hindu scripture makes about the Uttarakurus. For instance the Aitareya Brahmana describes the land of the Uttarakurus as unconquerable by humans. And in this chapter of the Sabha Parva of the Mahabharata, Arjuna tries to conquer the land of the Uttarakurus but is told this by the guards at the border of the kingdom:
O son of Pritha, this country can be never conquered by thee. If thou seekest thy good, return hence. He that entereth this region, if human, is sure to perish. We have been gratified with thee; O hero, thy conquests have been enough. Nor is anything to be seen here, O Arjuna, that may be conquered by thee. The Northern Kurus live here. There cannot be war here. Even if thou enterest it, thou will not be able to behold anything, for with human eyes nothing can be seen here.
The part in bold is relevant. I find all this strange, since there are now plenty of humans who live on the other side of the Himalayas. But regardless, even if it is true that the land of the Uttarakurus cannot be perceived by humans, why is it that their existence cannot be proven by inference? If you went, like Arjuna, to the border of the kingdom and spoke to the guards, couldn't you infer the existence of the Uttarakurus from the existence of their guards?