Because this sentence does not establish monotheism...

Because this sentence does not establish monotheism; even the polytheists say that He is one God, in the same way as each of their deities is one god, Nor would have the sentence, “And your God is one”, established monotheism. Because it could be imagined that He is one in the species of divinity. People say, when they enumerate the species of animals: Horse is one; mule is one - although horse and mule are manifold in number.

That is why the Qur'an said: "And your God is one God." "One God" (in contrast to two or more gods) is made predicate of "Your God". In this form the sentence clearly establishes the belief of monotheism, by restricting the godhead to one of the gods in which they believed. QUR'AN: there is no god but He: It further emphasizes the clear declaration of the preceding sentence about monotheism and negates every possible misinterpretation or superstition.

The negative particle "la" (= no) is used here to negate the genes; ilah (= god) denotes here real and actual God. The sentence has an implied predicate "existent", and the meaning will be as follows: There is no real and actual god existing "but He". The pronoun "He", used in place of the proper name, Allah, is in nominative, not subjunctive case. Therefore, the word "but" is not used here as particle of exception; rather it is an adjective in the sense of "other than".

The complete sentence, thus, means: There is no real god, other than Allah, existing. The sentence therefore aims at repudiation of gods, other than Allah - the deities, which had no real existence outside the imagination of their worshippers. It does not aim at refuting other deities and proving the existence of Allah. as many scholars have thought. Our explanation is supported by the fact that the sentence needs only a negative mode, and not a negative followed by affirmative.

Only repudiation of other imaginary deities is enough to confirm the Oneness of Allah in His godhead. Moreover, the Qur'an treats the existence of Allah as a self-evident truth, which needs no proof or argument. The Qur'an only cares to affirm and prove His attributes; for example, it only proves that Allah is One; that He is the Creator, the Knower, the Powerful and so on. Question: You say that the sentence has an implied predicate existent (or some other word of the same meaning).

If so, then it would only negate the actual existence of other deities but not the "possibility" of their existence.