Tafsir of Al-Isra 17:42

Say: In demonstrating the falsehood of that from another perspective, {if there were with Him}—that is, Exalted and Majestic is He in existence—{gods as they say}—meaning the polytheists collectively. Hamzah, al-Kisa'i, and Khalaf read it with a ta as the third letter, addressing them directly. Both expressions are common in such a context; for when someone is commanded to convey speech to another, the person to whom it is conveyed is absent at the time of the commander's speech, but becomes an addressee upon the delivery. If the first state is considered, the third person is appropriate; if the second is considered, address is appropriate. They read similarly thereafter. Nafi', Ibn 'Amir, and Abu Bakr from 'Asim read here with a ta, and elsewhere with a ya as the last letter, implying that He, Exalted be He, is declaring Himself transcendent from the beginning, without the Messenger (peace and blessings be upon him) being commanded to say it to them. The kaf is in the accusative position as an adjective for an elliptical verbal noun, meaning: "being similar to what they say." Similarity, according to what has been said, means agreement and correspondence.

{Then they would have sought}—the apodosis to "if" (law) regarding their claim that there are gods with Allah, Exalted is He—{to the Possessor of the Throne}—meaning to the One who possesses absolute sovereignty and Lordship—{a way}—by way of striving and resistance, as is the established custom among kings. This is an indication of the proof of mutual hindrance (tamānu'), similar to His saying, Exalted is He: "If there were within them [the heavens and earth] gods besides Allah, they both would have been ruined." This is done by formulating a disjunctive syllogism in which the negation of the consequent is excluded to yield the negation of the antecedent, which is the required conclusion. Its detailed explanation will come, God willing, in its proper place. Sa'id ibn Jubayr held this view, as reported from him by Ibn Abi Hatim.

According to Mujahid and Qatadah, the meaning is: "Then they would have sought approach and nearness to Him, Exalted is He, through obedience, knowing His exaltation above them and His magnificence." This is like His saying, Exalted is He: "Those whom they invoke seek a means of access to their Lord." This is an indication of a categorical syllogism, as follows: If there were gods as you claim, they would have sought nearness to Him, Exalted is He; and anyone who is such is not a god; therefore, they are not gods. It has been said that the "if" (law) in the first interpretation denotes impossibility, while in the second, it is conditional, and the syllogism is composed of two premises: one conditional (based on agreement) and one categorical.