Anavastha (Sanskrit: अनवस्था) is a Sanskrit nominal compound derived from the verb Stha (meaning standing, resting, grounded or founded). This expression literally means - that which does not stand down, non-resting, unstable, holding no definite position, un-grounded or without foundation, it also means unsettled condition or character and absence of finality or conclusion. As a philosophical term it refers to the non-finality of a proposition or endless series of statements or regressus ad infinitum (infinite regress). In Hindi language, as a noun Anavastha means Nothingness.
In Indian thought and Indian logic Anavastha is an important doctrine. All major schools of philosophy have examined and commented upon this concept and laid down guidelines so as to avoid the endless series of statements and propositions and the non-finality of those propositions. Certain aphorisms of Pāṇini, in his Ashtadhyayi indicate that asiddhatva leads to anavastha since rules which cause endless repetition of application cannot be there because application of a rule should certainly result in finality. The word अत्र atra of Sutra 6.4.22 indicates that two rules must have the same आश्रय āśraya or place of operation but where their places of operation are different they are not asiddha to each other.
The automatic application of sutras (rules of grammar) to take place without generating unintended results requires the establishment of a particular sequence among the rules and also the provision for cyclical application as well as blocking of some rules whenever it is desirable to do so. Panini orders rules and methods for their activation, reactivation and non-activation, and provides that the results brought about by some rules will not be 'known' to certain other rules, so that the question of these other rules becoming activated does not arise. The best example of the application of this method is known as Asiddhatva. He uses the concept of Asiddhatva to prevent the application of a rule on the substitute, to enable its application on a substituent and to mandate its application. According to Kiparsky’s definitions, Asiddhatva implies 'no order of taking effect' since asiddha means 'not having taken effect'.
The Upanishads speak about the two-fold Brahman, the one with attributes called the Saguna Brahman, and the other without attributes called the Nirguna Brahman only to deny and accept these two to state that Brahman is One. Brahman is called Nirguna because Brahman has not the three Gunas of Prakrti, and not because Brahman has got no gunas absolutely; in order to prove the substantive existence of Brahman (prameya), Brahman is called Saguna even though there is absence of Gunas in Brahman (aprameya). Brahman is One, and Oneness cannot be confounded with non-oneness; also oneness does not require another oneness to differentiate through second oneness or a third to differentiate the second oneness, otherwise there will be no end or conclusion. This fallacy is Anavastha or infinite regress. The Vedas advise that Brahman must be looked at in one and one mode only. In created things differences are of three kinds – 1) Existing in oneself, 2) difference in species and 3) difference in genus. In three words denoting a) 'oneness of Brahman', the svajatiya-bheda, b) 'restriction', the svagata-bheda and 3) 'rejection of duality', the vijatiya-bheda, these three differences are negated by the Sruti texts (Panchadasi Stanzas II.20&21). The created things are many, a chain of causes and effects is also present, but to avoid the fallacy of anavastha, it is necessary to consider Brahman as the root cause.