This prakṛti, however, is the eternal state which is not an emanation itself but the basis and source of all other emanations. The liṅga and the aliṅga have thus been compared in the _Kārikā_: “_hetumadanityamavyāpi sakriyamanekāśritaṃ liṅgaṃ sāvayavam paratantraṃ vyaktaṃ viparītamavyaktaṃ_.” The liṅga has a cause, it is neither eternal nor universal, but mobile, multiform, dependent, determinate, and possesses parts, whereas the aliṅga is the reverse. The aliṅga or prakṛti, however, being the cause has some characteristics in common with its liṅgas as distinguished from the purushas, which are altogether different from it. Thus the _Kārikā_ says: “_triguṇamaviveki vishayaḥ sāmānyamacetanaṃ prasavadharmi vyaktaṃ tathā pradhānaṃ tadviparītastathā pumān_.” The manifested and the unmanifested _pradhāna_ or _prakṛti_ are both composed of the three guṇas, non-intelligent, objective, universal, unconscious and productive. Soul in these respects is the reverse. We have seen above that prakṛti is the state of equilibrium of the guṇas, which can in no way be of any use to the purushas, and is thus held to be eternal, though all other states are held to be non-eternal as they are produced for the sake of the purushas. The state of prakṛti is that in which the guṇas completely overpower each other and the characteristics (_dharma_) and the characterised (_dharmī_) are one and the same. Evolution is thus nothing but the manifestation of change, mutation, by the energy of rajas. The rajas is the one mediating activity that breaks up all compounds, builds up new ones and initiates original modifications. Whenever in any particular combination the proportion of sattva, rajas or tamas alters, as a condition of this alteration, there is the dominating activity of rajas by which the old equilibrium is destroyed and another equilibrium established; this in its turn is again disturbed and again another equilibrium is restored. Now the manifestation of this latent activity of rajas is what is called change or evolution. In the external world the time that is taken by a paramāṇu or atom to move from its place is identical with a unit of change.[23] Now an atom will be that quantum which is smaller or finer than that point or limit at which it can in any way be perceived by the senses. Atoms are therefore mere points without magnitude or dimension, and the unit of time or moment (_kshaṇa_) that is taken up in changing the position of these atoms is identical with one unit of change or evolution. The change or evolution in the external world must therefore be measured by these units of spatial motion of the atoms; i.e. an atom changing its own unit of space is the measure of all physical change or evolution.