Sankhya or Samkhya is the oldest school of philosophy. The word samkhya literally means experiential or relating to numbers .In the context of ancient Indian philosophies, Samkhya refers to the philosophical school based on systematic enumeration and rational interpretation of the world surrounding us. The Samkhya system is defined in above way because it clearly 'enumerates' twenty five (25) Tattvas (elements or true principles) and propagates the ultimate objective of emancipation of the twenty-fifth Tattva,which is the Puruṣha (soul, spirit etc).In this way Samkhya is a dualist theory and believes in the existence of two realities ,which are Puruṣha (Soul) and Prakarti (matter) in the universe.Puruṣha when is bonded to Prakriti in any degree is termed as ‘Jiva’. This ‘interection’ of Purusha and Prakarti is responsible for emergence of different compounds.The first one is Buddhi (Intellegence) and Ahankara (Ego or sense of existence of self). The universe is described by this school as one created by interaction of Purusha and Prakriti resulting in various permutations and combinations of variously enumerated elements like senses, feelings, activity and mind. During the state of imbalance,purushya remains in bondage, due to its false identification of self with Chitta. The end of this imbalance or bondage is referred as liberation or Moksha by Samkhya School.
Samkhya is known for its theory of Gunas (qualities, basic tendencies) and these Gunas are of three types. According to Samkhya the Universal Energy, has three modes (or Gunas) of manifestation, which are Sattva, Rajas and Tamas. Sattva guna indicates being positive, compassionate, illuminating, Rajas guna is one indicative of movement, activity, passion, potentially leading to good or bad and Tamas being associated with negatives like destruction, darkness, ignorance, inertia laziness. Everything, all life forms and human beings, according to Samkhya posses these three Gunas, but in very different and distinct proportions. The interplay of these Gunas defines the character of someone or something and determines the course of life of someone. When these three universal vibrations are in equipoise, there is no action. It is only when there is a (Bikshob) disturbance in the equilibrium of these three gunas that (Shristi) evolution begins. Universal Energy or Prakriti (Nature) by its inherent nature is unconscious and only due to presence of the conscious Purusha (Soul) the evolution (transformation) begins. This theory of three Gunas given by Samkhya school is widely discussed and refined by various schools of Indian philosophies including its offshoots like Buddhism and Jainism. The diagram below gives a basic introduction of all the 24 elements believed in Sankhya system.

24 core principle of sankhya yog