Iranian linguist Ahmad Kasravi, in an article "Shemiran-Tehran", suggested that Tehran and Kehran mean "the warm place", and "Shemiran" means "the cool place". He listed cities with the same base and suffix and studied the components of the word in ancient Iranian languages, and came to the conclusion that Tehran and Kehran meant the same thing in different Iranian language families, as the constant "t" and "k" are close to each other in such languages. He also provided evidence that cities named "Shemiran" were cold, and those named "Tehran" or "Kehran" very hot. He considered other theories not considering ancient history of Iranian languages such as "Tirgan" theory and "Tahran" theory folk etymology.