Taj al-Din al-Subki, may God have mercy on him, authored his book, JAM 'AL-JAWAMI' (USUL AL-FIQH), to be a concise and inclusive of the issues of this science, by which students can dispense with anything else, he made a distinguished effort in it, which was witnessed by the great scholars of his time, yet it is not without criticism, or objection to some of its issues, especially in the field of defining jurisprudential terms; As it is required in the definition that it be inclusive of the descriptions of the defined, preventing others from entering it, and what came out of this principle is Al-Subki’s definition of the term (validity), where Al-Aizari objected to it that it is neither comprehensive nor prevented, Because validity means the effects on it, and we find in the definition of Al-Subki has Some traces were left behind with the validity of the contracts, and on the other hand, some traces were found with the invalidity of the contracts, and this constitutes a violation of the definition from the viewpoint of Al-Aizari, so discussions took place about it, and the answers came to clarify its truth, so I collected in this research what is related to this issue of sayings and evidence, In this research there was a clear treatment of this issue after presenting the definition, the reference to it, the answer and the discussion, and citing the words of the investigating scholars, then giving preference to the correct saying.