Reinöhl mentions that not only have the Dravidian languages borrowed from Sanskrit vocabulary, but they have also impacted Sanskrit on deeper levels of structure, "for instance in the domain of phonology where Indo-Aryan retroflexes have been attributed to Dravidian influence". Hock et al. quoting George Hart state that there was influence of Old Tamil on Sanskrit. Hart compared Old Tamil and Classical Sanskrit to arrive at a conclusion that there was a common language from which these features both derived – "that both Tamil and Sanskrit derived their shared conventions, metres, and techniques from a common source, for it is clear that neither borrowed directly from the other." Reinöhl further states that there is a symmetric relationship between Dravidian languages like Kannada or Tamil, with Indo-Aryan languages like Bengali or Hindi, whereas the same relationship is not found for non-Indo-Aryan languages, for example, Persian or English: "A sentence in a Dravidian language like Tamil or Kannada becomes ordinarily good Bengali or Hindi by substituting Bengali or Hindi equivalents for the Dravidian words and forms, without modifying the word order; but the same thing is not possible in rendering a Persian or English sentence into a non-Indo-Aryan Shulman mentions that "Dravidian nonfinite verbal forms (called in Tamil) shaped the usage of the Sanskrit nonfinite verbs (originally derived from inflected forms of action nouns in Vedic). This particularly salient case of the possible influence of Dravidian on Sanskrit is only one of many items of syntactic assimilation, not least among them the large repertoire of morphological modality and aspect that, once one knows to look for it, can be found everywhere in classical and postclassical Sanskrit". The main influence of Dravidian on Sanskrit is found to have been concentrated in the timespan between the late Vedic period and the crystallization of Classical Sanskrit. As in this period the Indo-Aryan tribes had not yet made contact with the inhabitants of the South of the subcontinent, this suggests a significant presence of Dravidian speakers in North India (the central Gangetic plain and the classical Madhyadeśa) who were instrumental in this substratal influence on Sanskrit. Influence Sanskrit has been the predominant language of Hindu texts encompassing a rich tradition of philosophical and religious texts, as well as poetry, music, drama, scientific, technical and others. It is the predominant language of one of the largest collection of historic manuscripts. The earliest known inscriptions in Sanskrit are