Qualities of the third and fourth class do not call for special treatment. In the third class, Aristotle’s distinction between ποιότητες παθητικαί (_qualitates passibiles_) and πάθη (_passiones_) is based upon the relatively permanent or transient character of the quality in question. The transient quality, such as the blush produced by shame or the pallor produced by fear, would be a _passio_;(329) whereas the more permanent quality, such as the natural colour of the countenance, would be a _passibilis qualitas._ The “passions” or sensible changes which result from certain conscious states, and affect the organism of the sentient living being, are included in this class as _passiones_; while the visible manifestations of more permanent mental derangement or insanity would be included in it as _passibiles qualitates_. We may, perhaps, get a fairly clear and comprehensive notion of all that is contained in this class as “sensible qualities” by realizing that these embrace whatever is the immediate _cause_ or the immediate _result_ of the _sense modification involved in any act or process of sense consciousness_. Such “sensible qualities,” therefore, belong in part to the objects which provoke sense perception, and in part to the sentient subject which elicits the conscious act. One of the most important problems in the Theory of Knowledge, and one which ramifies into Cosmology and Psychology, is that of determining the precise significance of these “sensible qualities,”—and especially in determining whether they are qualities of an extramental reality, or merely states of the individual mind or consciousness itself. _Form_ or _figure_, which constitutes the fourth class of quality, is a mode of the quantity of a body, being merely the particular surface termination of its extension or volume. Considered as a mode of abstract or mathematical quantity, it belongs to the domain of mathematics. Considered in the concrete body, it is the physical, sensible form, shape, or figure, of the latter; and here it may be either natural or artificial, according as it results from the unimpeded action of natural forces or from these forces as manipulated and directed by intelligent agents. It is worthy of special note that while extension or volume is indicative of the _material_ principle of corporeal substances, the figure or shape naturally assumed by this volume is determined by their _formative_ principle, and is thus indicative of their specific nature. This is already noticeable in the inorganic world, where many of the chemically different substances assume each its own distinctive crystalline form. But it is particularly in the domains of botany and zoology that the natural external form of the living individual organism is recognized as one of the most important grounds of its classification and one of the surest tests of its specific nature.(330)