In this study, the conceptual principles underlying the logical formalization of Avicenna’s Proof of the Truthful (Burhān al-Ṣiddīqīn) in the Kitāb al-Najāt are subjected to a critical re-examination using first-order predicate logic, with reference to two articles by Ranjbar and colleagues. The author maintains that the conceptual principles of the proof—among them the concepts of existence, necessity, possibility, causality, and the causal series—require a deeper analysis.



In the analysis of the concept of existence, it is shown in the first article that failing to adopt a correct stance regarding quantifiers can undermine the truth of some premises and the conclusion of the proof. Moreover, the position adopted by the authors in the second article, given their analysis of the concept of “Necessary Existent,” leads to the invalidation of the proof. This is because, in that case, the conclusion of the proof is imposed upon it as a linguistic presupposition, and, in effect, formulating the negation of the conclusion within the language becomes impossible.



An analysis of the concepts of the Necessary Existent and the Possible Existent reveals that the definitions provided are neither exhaustive of instances nor exclusive of non-instances, and that without offering an analysis of the second-order predicates of necessity and possibility, resolving this problem is impossible.



Finally, it is shown that the predicate of causality can be presented with a higher degree of analysis, such that—while satisfying the necessary conditions—it is also possible to arrive at sufficient conditions in its definition. Regarding the concept of the complete causal series of possible beings, certain objections are raised, including the failure of the analysis of the complete causal series to exclude the inclusion of an empty series; these objections are addressed by offering alternative analyses.