The 24 principles of Prakriti according to Sankhya are constituted of Prakriti with its 3 modes, plus 10 principles that form the “objective” manifestation (5 elements and 5 properties) and 13 principles that form the “subjective” manifestation. These thirteen are Buddhi (also known as Mahat), Ahankara and Manas, plus 5 senses of perception and 5 senses of action.
The 5 senses of perception are the ones that perceive the 5 properties of the 5 elements, namely “…hearing, touch, sight, taste and smell, which make the five properties of things their respective objects…”
There are also 5 senses of action which “…specialises certain necessary vital functions of reaction by aid of the five active senses which operate for speech, locomotion, the seizing of things, ejection and generation.”
These 10 senses are in their essence tools of the principle of Manas, translated as “mind” which “….is the original sense which perceives all objects and reacts upon them; for it has at once an inferent and an efferent activity, receives by perception what the Gita calls the outward touches of things, bahya sparsa, and so forms its idea of the world and exercises its reactions of active vitality.
Ahankara, or ego-sense, “…is the subjective principle in Buddhi by which the Purusha is induced to identify himself with Prakriti and her activities.” The ego-sense provides “continuity” to the experience as well as a “centralising” action.
Buddhi, or Mahat, is “…the discriminating principle, is at once intellience and will; it is that power in Nature which discriminates and co-ordinates.”
According to Sankhya, all of these subjective principles are part of the mechanical Nature, Prakriti, and are subject to the action of the 3 gunas, or “modes” of Nature.
While we may want to attribute these subjective powers to the Purusha, or Soul, Sankhya disagrees. Sri Aurobindo points out that modern science has come to a similar conclusion when viewing the inherent intelligence in the material world: “Even in the mechanical action of the atom there is a power which can only be called an inconscient will and in all the works of Nature that pervading will does inconsciently the works of intelligence.”
Mental intelligence has basically the same functioning. Sankhya finds a solution to the mystery of how mechanical Nature can seemingly act with conscious will and intelligence. “It is because of the reflection of Prakriti in Purusha; the light of consciousness of the Soul is attributed to the workings of the mechanical energy and it is thus that the Purusha, observing Nature as the witness and forgetting himself, is deluded with the idea generated in her that it is he who thinks, feels, wills, acts, while all the time the operation of thinking, feeling, willing, acting is conducted really by her and her three modes and not by himself at all.”
Sri Aurobindo, Essays on the Gita, First Series, Chapter 8, Sankhya and Yoga, pp. 67-68,