At the heart of philosophical sciences, classical logic aims to derive the unknown from the known. To achieve this goal, it has established a systematic method while making valid and correct inferences. This method is "burhān," the most important of the five arts. Burhān is a syllogistic form whose premises and conclusion depend on specific conditions. This form provides us with certain rational knowledge. Consequently, Ibn Sīnā (Avicenna) (d. 1037) constructed his philosophical methodology using this art. In demonstrative reasoning, the objective is to attain a definite, sound, and necessarily correct conclusion. Additionally, Ibn Sīnā's theory of demonstration shaped his logical way of thinking. Moreover, Aristotle's (384–322 BCE) book Posterior Analytics had a significant influence on Ibn Sīnā's theory of demonstration. Therefore, within the context of Ibn Sīnā's theory, there are points of convergence and divergence with the preceding Aristotelian tradition. Furthermore, his aforementioned view on demonstration has guided and influenced subsequent logicians. Also, what are the types of burhān as the most certain and powerful form of proof? How is the epistemic value of these types determined? Since demonstrative reasoning is necessary for proofs in all sciences, how should its conditions be prepared? The study seeks answers to such questions. Finally, based on the data obtained, Ibn Sīnā's theory of demonstration will be systematically presented within a general framework, aiming to identify his contributions to the subject.

Keywords: Logic, Ibn Sīnā (Avicenna), burhān (demonstration), certainty, proof.