About Verbs ？t- and ？t- in Old Turkic

In Old Turkic, there are both ？t- and ？t-, which means ‘to sing, to make sounds (for animals)’. These are more prevalent in that period, but the use of ？t- has diminished over time and has left its place to the ？t-. The historical phonetics does not provide us any conclusive evidence whether there is a sound shifting at the beginning of the word like /？-/ > /？-/. For this reason, it is necessary to evaluate the two verbs separately. The existence of two verbs as a difference today in Turkic languages support our hypothesis