“Of the six orthodox philosophies of Vedic tradition — Sāṅkhya, Yoga, Nyāya, Vaiśeṣika, Mīmāṁsā and Vedānta — only the Vedānta of Bādarāyaṇa Vyāsa is free of error, and even that only as properly explained by the bona fide Vaiṣṇava ācāryas. Each of the six schools, nonetheless, makes some practical contribution to Vedic education: atheistic Sāṅkhya explains the evolution of natural elements from subtle to gross, Patañjali’s yoga describes the eightfold method of meditation, Nyāya sets forth the techniques of logic, Vaiśeṣika considers the basic metaphysical categories of reality, and Mīmāṁsā establishes the standard tools of scriptural interpretation. Apart from these six, there are also the more deviant philosophies of the Buddhists, Jains and Cārvākas, whose theories of voidism and materialism deny the spiritual integrity of the eternal soul.
Ultimately, the only perfectly reliable source of knowledge is God Himself. The Personality of Godhead is avabodha-rasa, the infinite reservoir of unfailing vision. To those who depend on Him with absolute conviction, He grants the divine eye of knowledge. Others, following their own speculative theories, must grope for the truth through the obscuring curtain of Māyā.”
Source:A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Tenth Canto, Chapter 87 – Text 25