The theory of Acquisition (Kasb) was proposed by Abu al-Hasan al-Ash'ari and was accepted by the majority of Sunnis. In addition to the traditionary evidences, 'Asha'ira scholars stated various rational evidences such as the impossibility of the combination between two causes for one effect, referring to the positivity of the attribute of omniscience and will and power, and the fallacy necessities of the opponent theory of Acquisition (Kasb). The author of this article if to explain and criticize the most important rational evidence of Asha'irah and will demonstrate that not only the the rational evidences of 'Asha'irah are defected, but also the theory of Acquisition (Kasb) is an irrational theory that is also in contrary with reason and conscience.