With Sāṃkhya-Yoga, sattva, rajas and tamas are substantive entities which compose the reality of the mental and the physical.[4] The mental and the physical represent two different orders of modifications, and one is not in any way superior to the other. As the guṇas conjointly form the manifold without, by their varying combinations, as well as all the diverse internal functions, faculties and phenomena, they are in themselves the absolute potentiality of all things, mental and physical. Thus Vyāsa in describing the nature of the knowable, writes: “The nature of the knowable is now described:—The knowable, consisting of the objects of enjoyment and liberation, as the gross elements and the perceptive senses, is characterised by three essential traits—illumination, energy and inertia. The sattva is of the nature of illumination. Rajas is of the nature of energy. Inertia (tamas) is of the nature of inactivity. The guṇa entities with the above characteristics are capable of being modified by mutual influence on one another, by their proximity. They are evolving. They have the characteristics of conjunction and separation. They manifest forms by one lending support to the others by proximity. None of these loses its distinct power into those of the others, even though any one of them may exist as the principal factor of a phenomenon with the others as subsidiary thereto. The guṇas forming the three classes of substantive entities manifest themselves as such by their similar kinds of power. When any one of them plays the rôle of the principal factor of any phenomenon, the others also show their presence in close contact. Their existence as subsidiary energies of the principal factor is inferred by their distinct and independent functioning, even though it be as subsidiary qualities.”[5] The Yoga theory does not acknowledge qualities as being different from substances. The ultimate substantive entities are called guṇas, which as we have seen are of three kinds. The guṇa entities are infinite in number; each has an individual existence, but is always acting in co-operation with others. They may be divided into three classes in accordance with their similarities of behaviour (śīla). Those which behave in the way of intellection are called _sattva_, those which behave in the way of producing effort of movement are called _rajas_, and those which behave differently from these and obstruct their process are called _tamas_. We have spoken above of a primal cause _prakṛti_. But that is not a separate category independent of the guṇas. Prakṛti is but a name for the guṇa entities when they exist in a state of equilibrium. All that exists excepting the purushas are but the guṇa entities in different kinds of combination amongst themselves. The effects they produce are not different from them but it is they themselves which are regarded as causes in one state and effects in another. The difference of combination consists in this, that in some