Samkhya

Samkhya is one of the six schools of Indian philosophy, meaning "counting" or "reckoning," which is understood by 25 principles (tattvas) that explain all of existence and reality.  Sankhya is a dualist philosopy believing there is higher spiritual beief/conciousness and a groundedness in natuure which which Yoga and Ayurveda both share.

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 Samkhya 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 create disturbances, leading to 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 Samkhya philosophy are Purusha (the highest consciousness) and Prakriti (nature). They are experienced through the connection of Mahat (intelligence), Ahamkara (ego & I awareness), and Manas (mind), which process input via the Five Sense Organs (eyes, ears, nose, skin, tongue), the Five Organs of Action (hands, feet, speech, elimination, and procreation), the Five Subtle Senses (sound, touch, form, taste, and smell), and the Five Elements in Nature (ether, air, fire, water, and earth).