The methods of determining the Imam, with the aim of establishing the legitimacy of the Imam and the caliph after the Prophet, have always been of great importance among Muslim thinkers, and works have been written since ancient times concerning the conditions and methods for determining or recognizing the Imam. By the method of determining the Imam is meant the ways by which the Imam’s rule would acquire legitimacy. Therefore, the issue of the method of determining the Imam has gained importance among different schools, and, as al-Shahrastani acknowledges, no religious principle in Islam has been fought over with the sword as much as the Imamate. The necessity of this study stems from the fact that the textual designation and choice as methods of determining the Imam have been subject to a compound consensus among Muslim thinkers, and this article seeks to critique the theory of choice. Consequently, by outlining the inevitable consequences of the theory of choice, the only method that should be accepted as a consensual method is designation by God or the Noble Prophet of Islam. Following this, the legitimacy of the rule of the caliphs—which, from the perspective of the overwhelming majority of Muslim scholars, is necessary for a ruler—will be evaluated with regard to the Rightly Guided Caliphs.