The third aspect is the aspect of tanmātras, which are the causes of the atoms or paramāṇus. Their fourth aspect is their aspect of guṇas or qualities of illumination, action, inertia. Their fifth aspect is that by which they are serviceable to purusha, by causing his pleasurable or painful experiences and finally his liberation. Speaking of aggregation with regard to the structure of matter, we see that this is of two kinds (1) when the parts are in intimate union and fusion, e.g. any vegetable or animal body, the parts of which can never be considered separately. (2) When there are such mechanical aggregates or collocations of distinct and independent parts _yutasiddhāvayava_ as the trees in a forest. A dravya or substance is an aggregate of the former type, and is the grouping of generic or specific qualities and is not a separate entity—the abode of generic and specific qualities like the dravya of the Vaiśeshika conception. The aspect of an unification of generic and specific qualities seen in parts united in intimate union and fusion is called the dravya aspect. The aggregation of parts is the structural aspect of which the side of appearance is the unification of generic and specific qualities called the dravya. The other aggregation of yutasiddhāvayava, i.e. the collocation of the distinct and independent parts, is again of two kinds, (1) in which stress may be laid on the distinction of parts, and (2) that in which stress is laid on their unity rather than on their distinctness. Thus in the expression mango-grove, we see that many mangoes make a grove, but the mangoes are not different from the grove. Here stress is laid on the aspect that mangoes are the same as the grove, which, however, is not the case when we say that here is a grove of mangoes, for the expression “grove of mangoes” clearly brings home to our minds the side of the distinct mango-trees which form a grove. Of the gross elements, ākāśa seems especially to require a word of explanation. There are according to Vijñāna Bhikshu and Nāgeśa two kinds of ākāśa—kāraṇa (or primal) and kārya (atomic). The first or original is the undifferentiated formless tamas, for in that stage it has not the quality of manifesting itself in sounds. This kāraṇa later on develops into the atomic ākāśa, which has the property of sound. According to the conception of the purāṇas, this karyākāśa evolves from the ego as the first envelope of vāyu or air. The kāraṇakāśa or non-atomic ākāśa should not be considered as a mere vacuum, but must be conceived as a positive, all-pervasive entity, something like the ether of modern physicists.