We have seen that the As̱ẖ‘arite theory of knowledge drove them to hold that individual essences of various things are quite different from each other, and are determined in each case by the ultimate cause--God. They denied the existence of an everchanging primary stuff common to all things, and maintained against the Rationalists that existence constitutes the very being of the essence. To them, therefore, essence and existence are identical. They argued that the Judgment, "Man is animal", is possible only on the ground of a fundamental difference between the subject and the predicate; since their identity would make the Judgment nugatory, and complete difference would make the predication false. It is, therefore, necessary to postulate an external cause to determine the various forms of existence. Their opponents, however, admit the determination or limitation of existence, but they maintain that all the various forms of existence, in so far as their essence is concerned, are identical--all being limitations of one Primary substance. The followers of Aristotle met the difficulty suggested by the possibility of synthetic predication, by advocating the possibility of compound essences. Such a judgment as "Man is animal", they maintained, is true; because man is an essence composed of two essences, animality and humanity. This, retorted the As̱ẖ‘arite, cannot stand criticism. If you say that the essence of man and animal is the same, you in other words hold that the essence of the whole is the same as that of the part. But this proposition is absurd; since if the essence of the compound is the same as that of its constituents, the compound will have to be regarded as one being having two essences or existences. It is obvious that the whole controversy turns on the question whether existence is a mere idea or something objectively real. When we say that a certain thing exists, do we mean that it exists only in relation to us (As̱ẖ‘arite position); or that it is an essence existing quite independently of us (Realist position)? We shall briefly indicate the arguments of either side. The Realist argued as follows:--