One of the most important sources on which human beings rely on for cognitive construction is rational argument. This argument has been the subject where a large number of scholars and researchers debate on. Some of them deny it, whereas others believe in it and rely on it in their works. As a result, this argument has become the subject of continuous deliberation among Muslim scholars, whether or not to make use of it for deriving the legal sub-rulings. Sunni scholars depend on it, although it would not lead to certainty. However, they reso
rt to analogy, approval and public welfare, whereas Twelver Shiite scholars deny the probable rational argument with all its sub-divisions, following the true traditions transmitted to them from their imams. Yet, they differ on that which leads to certainty (concerning rational argument). So, some deny it, like the Akhbarites (traditionalists), and others take it as one of the sources of legislation for deriving legal rulings, such as the Usulites.Because of the importance of the topic, we have tried, in this study, to shed light on this argument and show the point of disagreement between Twelver Shiite scholars, quoting the sayings, arguments and discussions of both parties, and then, getting to the right conclusion due to our own opinion. In all that, we have followed the inductive analytical approach. We have extrapolated the sayings of the scholars of both fundamentalist school and Akhbarite school as possible due to the limitation of the article, and then to judge between them.