There is no unambiguous evolution of Kurdish from Middle Iranian, as "from Old and Middle Iranian times, no predecessors of the Kurdish language are yet known; the extant Kurdish texts may be traced back to no earlier than the 16th century CE." Ludwig further states: "Linguistics itself, or dialectology, does not provide any general or straightforward definition of at which point a language becomes a dialect (or vice versa). To attain a fuller understanding of the difficulties and questions that are raised by the issue of the “Kurdish language,” it is therefore necessary to consider also non-linguistic factors." ↑ Izady, Mehrdad R (1992).