The Development of the Simple rule of Truth in Islamic Philosophy and its Achievements and Results

The "the simplicity of the reality (al-ḥaqīqa) of all things and the licks of something from them" rule is one of the most important topics Theology in particular that Mulla Sadra claims that no one other than Plotinus and he found out about it. And also the development of this rule, what philosophical problems has it solved and what achievements has it brought about in Sadra’s philosophy? Considering that this rule can be understood in the realm of unity in plurality and the realm of plurality in unity, this article is based on it by proving that Mulla Sadra, in understanding the principle of this rule, is indebted to the verses, hadiths, and intuitions of mystics in both realm, has tried to expose the development of this rule among the philosophers before Mulla Sadra to criticism and analysis in a descriptive and analytical method. Therefore; Plotinus tried to express the content of this rule in both realms. But Farabi, Suhrawardi and Mirdamad played a role in the development of this rule only in the realm of plurality in unity, ignoring their foundations. Also, Mulla Sadra and his followers have used this rule in both realms in the course of the development of the Transcendent theosophy in many cases, such as the relationship between the God and its knowledge, or the relationship between the soul and its powers.