Likewise, the quiddity that resides in the intellect is nothing but its mental existence, and the entity that exists outside the mind is the quiddity that exists externally. Just as there is no existent in the mind other than that very quiddity, so too there is no quiddity existing outside the mind except the concrete subject of which the quiddity is predicated.
In the same vein, the error of the ahl al-ḥāl falls under this heading. These two kinds of misguidance have entangled groups of exceptionally intelligent men: they seized upon terms that, whether in the intellect or in external reality, stand on an equal footing with respect to affirmation and denial, then arbitrarily declared some affirmed and others denied. Their error in affirmation and negation mirrors their error concerning universality and particularity.
It is well known that propositions, in their essence, do not differ simply by being affirmative or negative, universal or particular. Yet they slipped in affirmation and negation just as they slipped in universality and particularity, owing to the ambiguity inherent in language: one of the two names tends to be dominated by one meaning, the other by a different meaning. If you wish the doubt to vanish, examine the meanings of the terms and leave aside the fruitless verbal wrangling. Take the meaning of this term with respect to its scope—general or particular—and its affirmation or denial, both in the mind and in external reality; then do the same with the other term. You will discover that they have drawn a distinction between things that are, in fact, identical.
The very foundation of demonstrative reasoning is to treat like cases alike. If, at the root of the syllogism they brandish as their proof, they have already discriminated between identical cases, they have erected the edifice of their knowledge on the brink of a crumbling cliff, and it collapses with them into the Fire of Hell. Allah does not guide a wrongdoing people, for drawing distinctions between things that are alike is one (1) form of injustice.