Al-Ghazali mentions three methods of proof in his al-Iqtisad fil-I'tiqad, particularly in its fourth introduction. He summarized them basically from various methods which had been used or mentioned in the earlier work of Kalam. These three methods, according to al-Ghazali, are clear, perceivable, and sufficient for people to acquire knowledge and to understand issues related to their faith, at least from the theological point of view. This article presents the methods together with an English translation of the related text from al-Iqtisad fil-I'tiqad. It also proposes that these methods could be widened in scope to apply to other fields of study. Keywords: Al-Ghazali; al-Iqtisad fil-i'tiqad; methods of proof; argumentation; Kalam.