Samkhya

Samkhya is one of the six schools of Indian philosophy, meaning "counting" or "reckoning," characterized by 25 principles (tattvas) that explain existence and reality. It incorporates the dualistic belief in Purusha (consciousness) and Prakriti (nature), which connects it to Yoga and Ayurveda.

Purusha is the principle of pure consciousness, spirit, and self, and is the passive witness/observer.

Prakriti is the principle of nature/matter that governs the evolution of the entire universe. 

In Sankhya philosophy, there are three qualities/tendencies (gunas) that manifest in the universe/nature, influencing the mind, emotions, and behavior: Sattva represents purity, clarity, and harmony; Rajas signifies activity, energy, and passion; and Tamas denotes darkness, heaviness, and inaction.

These three gunas exist in a state of balance in Prakriti, but are in constant flux; their manifestations in the universe and the human experience can result in disturbances, creating imbalance.  Ayurveda and Yoga utilize the five elements found in nature and the universe to bring balance when there is imbalance.

The 25 tattvas (principles) that make up Sankhya philosophy are (1) Purusha (highest consciousness) and (2) Prakriti (nature). They are experienced through the connection of (3) Buddhi (intelligence), (4) Ahamkara (ego & I awareness), and (5) Manas(mind), which process input via the (10) Five Sense Organs (eyes, ears, nose, skin, tongue), the (15) Five Organs of Action(hands, feet, speech, elimination, and procreation), the (20) Five Subtle Senses (sound, touch, form, taste, and smell), and the (25) Five Elements in Nature (ether, air, fire, water, and earth).