 Let us quickly review some other features of Nyāya-Vaiśeṣika atomism. First, like the four material elements, mind (manas) is also said to be of corporeal nature and atomic in magnitude though lacking in sensible quality. Material atoms have specific sensible qualities and so are called ‘bhūta’; both matter and mind are capable of movement and so designated ‘mūrta’. The four elements come closest to a scientific conception of matter. Second, all atoms are said to be quantitatively identical and qualitatively different. Two atoms belonging to different types can be easily differentiated by their specific attributes, but the problem arises while differentiating two atoms of the same type, say, two earth atoms. The Nyāya-Vaiśeṣikas therefore introduce in their ontology a unique objective principle called ‘viśeṣa’ (ultimate differentiator) for individuating atoms. Third, the wholes constituted by atoms are not mere conjunctions of atoms, but are new entities inhering in their own parts. Fourth, the atomic theory is intimately connected with their theory of causation. A cause has been defined in this system as an invariable, unconditional antecedent of an effect; an effect, on the other hand, is said to be the counter-correlative of a prior absence. A counter-correlative of any absence removes that absence. A pot is a counter-correlative of its prior absence because this absence of pot disappears as soon as the pot is produced. Every effect is preceded by its prior absence, so each effect is a new production. Such theory of causation is known as ārambhavāda, the theory that an effect always comes into existence out of a prior state of non-existence (as opposed to the theory of existent effect (satkāryavāda) advocated by the Sāṃkhya school). Causes are of two types: (a) common (sādhāraṇa) and (b) uncommon (asādhāraṇa). A common cause is uniformly present before the occurrence of any effect whatsoever and is necessary for effectuation as such; an uncommon cause is that which invariably and unconditionally precedes a particular effect. Common causes are space, time, accumulated merits and demerits of individual agents (adṛṣṭa), God, knowledge, desire and will (prayatna) of God, and prior absence (prāgabhāva). Uncommon causes are divided into three classes: (a) inherent (samavāyi), (b) non-inherent (asamavāyi) and (c) efficient (nimitta). Without entering into their technical definitions, let us understand them with the help of an example. Atoms are the inherent causes of the world, conjunctions of atoms are its non-inherent causes, and God and adṛṣṭa are its efficient causes. Fifth, admitting numbers as the cause of grossness of a triad shows that they have a capacious world-view where numbers can have causal effect on the physical world.