Abstract
The aim of the research is to track and study a phenomenon of the Arabic language, which was known to the authors of the language, ancient and modern, and it is the phenomenon of substitution between letters, and it was of interest to Arabic language scholars, and the people of the language wrote books and compilations, as most of the ancient compilations contained chapters and chapters devoted to substitution between Arabic letters This phenomenon was subject to criticism between acceptance and rejection by the people of the language. Because there are some mistakes in it, so they criticized it and corrected the wrong ones, and our scholars, old and new, took care of it, including the owners of dictionaries, as their works included criticisms of this phenomenon, and a statement of the most correct in the opinion of the critic. The places in which the substitutions were criticized, and because of their abundance, were selective choices, treated according to the old and modern dictionaries.
