Metaphysical Form in Ancient and Medieval Thought

The metaphysical notion of form (eidos, morphe, Gr.; idea, forma, species, Lat.), as it emerged in the works of Plato, must be carefully distinguished from the everyday notion from which it derived, namely, the shape or outer appearance of a thing as it presents itself to the eyes. The outer appearance of a mannequin, for instance, may be deceptively similar to that of a human being, yet, the form in the philosophical sense would be radically different for the two. The form of the thing in the philosophical sense is what determines the kind of thing it is, and so the kinds of properties it can or cannot have, and the kinds of things it can or cannot do or suffer. The mannequin, being a lifeless artifact, obviously cannot perform the characteristic operations any human being naturally can (unless prevented by some circumstance), such as walking, talking, begetting or giving birth to human offspring, and so forth. Therefore, a human being and a mannequin must have different forms. But does it follow that two individual human beings must have the same form? Two individual human beings are equally humans, and as such they equally have the same sort of characteristic operations and abilities. However, no two human beings have numerically the same operations and abilities. This author's activity of writing this article is not anybody else's activity, although another human being could perform exactly the same sort of activity. Still, the author's activity and the other person's activity are two, hence numerically distinct, activities, even if they are of the same sort. In the same way, the form on account of which the author has the ability to perform this activity is not numerically the same as the form on account of which another person would be able to perform the same sort of activity. So, there must be some numerically distinct individualized forms, namely, forms that individually determine one's essential abilities.