Scholastic Philosophy has generally adopted Aristotle’s division of qualities into four great groups:(327) (1) ἕξις ἢ διάθεσις, _habitus vel dispositio_; (2) δύναμις φυσικὴ ἢ ἀδυναμία, potentia _naturalis vel impotentia_; (3) ποιότητες παθητικαί καὶ πάθη, _potentiae passivae et passiones_; (4) μορφὴ ἢ σχῆμα, _forma vel figura_. St. Thomas offers the following ground for this classification. Since quality, he says,(328) is an accidental determination of the substance itself, _i.e._ of the perfection of its concrete existence and activity, and since we may distinguish four aspects of the substance: its nature itself as perfectible; its intrinsic principles of acting and receiving action, principles springing from the _formative_, specific constituent of its nature; its receptivity of change effected by such action, a receptivity grounded in the determinable or _material_ principle of its nature; and finally its quantity, if it be a corporeal substance,—we can likewise distinguish between (1) _acquired habits or dispositions_, such as health, knowledge, virtue, vice, etc., which immediately determine the perfection of the substance, disposing it well or ill in relation to its last end; (2) intrinsic _natural forces_, _faculties_, _powers of action_, _aptitudes_, _capacities_, such as intellect, will, imagination, instinct, organic vital forces, physical, chemical, mechanical energies; (3) states resulting in a corporeal being from the action of its _milieu_ upon it: the _passions_ and emotions of sentient living things, such as sensations of pleasure, pain, anger, etc.; the _sensible qualities_ of matter, such as colour, taste, smell, temperature, feel or texture, etc.; and, finally (4) the quality of _form or shape_ which is a mere determination of the quantity of a corporeal substance. This classification is not indeed perfect, for the same individual quality can be placed in different classes when looked at from different standpoints: heat, for instance, may be regarded as a _natural operative power_ of a substance in a state of combustion, or as a _sensible quality_ produced in that substance by the operation of other agencies. But it has the merit of being an exhaustive classification; and philosophers have not succeeded in improving on it.