Now from this view of the reality of the external world we are confronted with another question—what is the ground which underlies the manifold appearance of this external world which has been proved to be real? What is that something which is thought as the vehicle of such qualities as produce in us the ideas? What is that self-subsistent substratum which is the basis of so many changes, actions and reactions that we always meet in the external world? Locke called this substratum substance and regarded it as unknown, but said that though it did not follow that it was a product of our own subjective thought yet it did not at the same time exist without us. Hume, however, tried to explain everything from the standpoint of association of ideas and denied all notions of substantiality. We know that Kant, who was much influenced by Hume, agreed to the existence of some such unknown reality which he called the Thing-in-itself, the nature of which, however, was absolutely unknowable, but whose influence was a great factor in all our experiences. But the _Bhāshya_ tries to penetrate deeper into the nature of this substratum or substance and says: _dharmisvarūpamātro hi dharmaḥ, dharmivikriyā eva eshā dharmadvārā prapañcyate_, _Vyāsa-bhāshya_, III. 13. The characteristic qualities form the very being itself of the characterised, and it is the change of the characterised alone that is detailed by means of the characteristic. To understand thoroughly the exact significance of this statement it will be necessary to take a more detailed review of what has already been said about the guṇas. We know that all things mental or physical are formed by the different collocations of sattva of the nature of illumination (_prakāśa_), rajas—the energy or mutative principle of the nature of action (_kriyā_)—and tamas—the obstructive principle of the nature of inertia (_sthiti_) which in their original and primordial state are too fine to be apprehended (_gunānāṃparamaṃ rūpaṃ na dṛshṭipathamṛcchati_, _Vyāsa-bhāshya_, IV. 13). These different guṇas combine in various proportions to form the manifold universe of the knowable, and thus are made the objects of our cognition. Through combining in different proportions they become, in the words of Dr. B. N. Seal, “more and more differentiated, determinate and coherent,” and thus make themselves cognisable, yet they never forsake their own true nature as the guṇas. So we see that they have thus got two natures, one in which they remain quite unchanged as guṇas, and another in which they collocate and combine themselves in various ways and thus appear under the veil of a multitude of qualities and states of the manifold knowable (_te vyaktasūkshmā guṇātmānaḥ_ [IV. 13] ... _sarvamidaṃ guṇānāṃ sanniveśaviśeshamātramiti paramārthato guṇātmānaḥ_, _Bhāshya_, _ibid._).