Why Correct: Samkhya, founded by Kapila around 6th century BCE, is the oldest systematic school of Indian philosophy, predating even Buddhism and Jainism.
Distractor Analysis: Yoga developed later as a practical application of Samkhya metaphysics. Vaisesika, founded by Kanada, emerged around 2nd century BCE. Karma Mimansa (Purva Mimamsa) focused on Vedic rituals and developed after Samkhya.
Takeaway: The six orthodox schools (Shad-darshanas) are Samkhya, Yoga, Nyaya, Vaisesika, Purva Mimamsa, and Uttara Mimamsa (Vedanta), with Samkhya being the foundational system.