This research deals with an important particularity having to do with the concept of Tayammum* which is a distinctive feature of the Islamic nation. It is considered one of the important matters of purification which is essential before performing Islamic prayer and a key condition without which prayer is rejected. The research comprises a foreword that shows the importance of the research, its approach and plan and a preface which comprises three subsections: First, the concept of interchangeability linguistically and traditionally, second, the concept of Tayammum linguistically and traditionally and the third concerns the proof of Tayammum's eligibility. The study also contains two sections; the first concerns the type of interchangeability and this is considered the core and the basis of this study, the second section studies the consequences of the dispute over this interchangeability, like performing Tayammum a while before it is time to pray, or praying behind imam who had performed Tayammum instead of ablution…etc.
In this study the researcher followed the solemn scientific approach which assumes collecting scientific material from its original sources and referring the Qur'anic Ayah's by the name and the number of the Surah , mentioning the prophetic traditions with stating its status was it from a source other than 'al Sahihain'. The researcher also mentioned the sayings of different scholars like the companions and the followers of the prophet (pbuh) as well as those of the known Imams of the precept (al Mathahib) in the disputable issues mentioned in this research in addition to giving proves to support each party and giving credit to one over the others. Finally he set an epilogue containing the main conclusions of this study