The tattwas (principles, evolutes, essences, "thatness") are twenty-five in number, and ennumerated in a particular sequence.
The first two are, purusha and prakriti, the original polarity of conscious subject and non-conscious object. In Samkhya creation comes about through an unfolding of the original prakriti. There is a sort of evolutionary emantion, with one principle in turn giving rise to the next.
The third tattwa, and the first evolute from the root-prakriti, is the pure intellect or Buddhi (equivalent perhaps to the Neoplatonic Nous). Since it preceeds ordinary awareness it could be understood as the principle of pure phenomenal consciousness. It is the locus of the bhavas or fundamental predispositions, such as dharma (virtue) and adharma (vice), jnana (knowledge) and ajnana (ignorance), etc; which in turn relate to the pratyaya-sarga or "intellectual creation".
The Buddhi is also known as Mahat, the "great one", or Mahatattwa, "great tattwa", the first emanation from the original Prakriti.
From Buddhi unfolds the principle of individuality or ego-sense; the sense of "I"-ness, the Ahamkara ("I-maker"). This is the source of all the subsequent tattwas. In some early writings it is divided into three aspects, a rajas aspect, a sattwa aspect, and a tamas aspect. The rajas aspect was called taijasa, meaning "shining" or "passionate", and constituted the fundamental ahamkara principle from which the other two derive. From the sattva aspect, called vaikrita ("modified") comes the mind or psyche (Manas), which is the faculty of thinking, memory, and so on.
Together with the Ahamkara and the Buddhi, the Manas constitutes the Antakarana or "inner organ" (i.e. consciousness or psyche). Also from the vaikrita ahamkara arise the Indriyas or "powers" or "capacities"; five of which are the five sense-powers or buddindriyas (seeing, hearing, etc), and five the five powers of action or karmendriyas (walking, speaking, etc). And from the tamas aspect of the ahamkara, called bhutadi or "origin of the elements", there unfolds the five "rudimentaries" or elements of subtle matter (Tanmatras); and finally from the latter the five elements of gross matter (Mahabhutas - the "great elements").
All this can be represented diagrammatically as follows:
(3) Buddhi [Intellect]
taijasa or rajas mode of Ahamkara
[Ego or "I"-ness]
vaikriti or sattwa mode of Ahamkara
bhutadi or tamas mode of Ahamkara
visible tattwas (21-25)
In this system of correspondences, all the principles from the Buddindriyas on are matched in a series of correspondences, for example, the sense-power of hearing is matched with the action-power of speaking (logically enough!), the tanmatra of "sound", and the gross element of "space" (because the Indians believed that sound was carried as vibrations through pure space, rather than through a medium like air).
The five gross elements are arranged in order of density, from space (akasha), which is most intangible, to earth, the most dense; an arrangement that first appeared in the Taittiriya Upanishad, and typifies the basic emanationist theme of the progression from most subtle to most gross and material. Later, with the development of Hatha Yoga and Shakta Tantric doctrines and the system of chakras (subtle centres of consciousness), this five-fold set of correspondences was used as a basis for defining the qualities of the first five chakras.
The final development of Indian emanationism is the Tantric cosmology of Kashmir Shaivism (later adopted by the Bengali branch of Shaktism or Tantra proper), which incorporates both Samkhyan emanationism and Advaita Vedantin Monism.