This course studies the following issues. The definition of the right and its types. The concept of al-Ta‘assuf, the abusing, its legal nature, the proofs of the legitimacy of this theory. A study to several examples from the practices of the companions of the Prophet Muhammad, peace be upon him, and the jurists which prove its authenticity, such as al-Dhara’i‘, al-Istihsan, al-Ba‘ith, the motive, and Qa‘idat al-Tahayyul. The standards of applying this theory and the scope of applying it.