Both philosophers agree on one thing: Form is able to classify all things in existence: a desk, a bathroom, a car, etc. are all their respective objects because they reflect themselves as such, but there are subtle differences in each of their theories. Plato claims that objects are only crude representations of their form. In Lindberg's Beginnings, Plato had drastically diminished the reality of the material world observed by the senses. Reality in its perfect fullness, Plato argued, is found only in the eternal forms, which are dependent on nothing else for their existence. .
The objects that make up the sensible world, by contrast, derive their characteristics and their very being from the forms; sensible objects exist only dependently. For example, when something that is considered beautiful, such as a flower, or painting, that characteristic is only physical and noticeable to the human senses, and the form of beauty is itself all around us, and unchanging. Many other factors can play a big part in the opinion of beauty to an object, such as age, or appeal. Plato concludes by saying that the Forms (in this particular example, beauty) is not accessible to the senses, and can only be understood by reason alone. The Form of Beauty also differs from a sensible object that is considered beautiful as it is forever beautiful no matter someone's opinion or the age of the object itself. .
Aristotle has a different opinion all together on the subject of form. Aristotle defined an object's form as not being something outside an object, but rather in the varied phenomena of the sense. Moreover, the traits that give an individual object its character do not have a prior and separate existence in a world of forms, but belong to the object itself.
Aristotle refutes Plato's definition believing it to be simply unclear. Instead, Aristotle defined an object's form as it's purpose which has been given to it by it's designer.
