              In the middle books of his Metaphysics, which contain some of his most complex and engaging investigations into basic being, Aristotle settles on form (Met. vii 17). A question thus arises as to how form satisfies Aristotle’s final criteria for substantiality. He expects a substance to be, as he says, some particular thing (tode ti), but also to be something knowable, some essence or other. These criteria seem to pull in different directions, the first in favor of particular substances, as the primary substances of the Categories had been particulars, and the second in favor of universals as substances, because they alone are knowable. In the lively controversy surrounding these matters, many scholars have concluded that Aristotle adopts a third way forward: form is both knowable and particular. This matter, however, remains very acutely  disputed.[23] 