mutation is brought about by the material principle of thofe two elements being deprived of the form of Water, and then affuming the form of Air. Privation, therefore, was a third principle oppofite to form, which entered into the generation of every Species, which was always from fome other Species. It was a principle of generation, but not of compofition, as is obvious.

The Stoics, whofe opinions were, in all the different parts of philofophy, either the fame with, or very nearly allied to those of Arif totle and Plato, though often disguised in very different language, held, that all things, even the elements themfelves, were compounded of two principles, upon one of which depended all the active; and upon the other, all the paffive powers of thefe bodies. The laft of thefe, they called the Matter; the first, the Caufe, by which they meant the very fame thing which Ariftotle and Plato understood, by their specific Effences. Matter, according to the Stoics, could have no existence separate from the cause or efficient principle which determined it to fome particular clafs of things. Neither could the efficient principle exist feparately from the material, in which it was always neceffarily embodied. Their opinion, therefore, fo far coincided with that of the old Peripatetics. The efficient principle, they faid, was the Deity. By which they meant, that

that it was a detached portion of the etherial and divine nature, which penetrated all things, that constituted what Plato would have called the specific Effence of each individual object; and fo far their opinion coincides pretty nearly with that of the latter Platonifts, who held, that the specific Effences of all things were detached portions of their created deity, the foul of the world; and with that of fome of the Arabian and Scholaftic Commentators of Aristotle, who held that the fubftantial forms of all things defcended from thofe Divines Effences which animated the Celestial Spheres. Such was the doctrine of the four principal Sects of the ancient Philofophers, concerning the specific Effences of things, of the old Pythagoreans, of the Academical, Peripatetic, and Stoical Sects.

As this doctrine of specific Effences feems naturally enough to have arifen from that ancient fyftem of Phyfics, which I have above defcribed, and which is, by no means, devoid of probability, fo many of the doctrines of that fyftem, which feem to us, who have been long accustomed to another, the most incomprehenfible, neceffarily flow from this metaphyfical notion. Such are thofe of generation, corruption, and alteration; of mixture, condenfation, and rarefaction. A body was generated or corrupted, when it changed its fpecific Effence, and paffed from one deno

mination to another. It was altered when it changed only fome of its qualities, but ftill retained the fame fpecific Effence, and the fame denomination. Thus, when a flower was withered, it was not corrupted; though fome of its qualities were changed, it still retained the specific Effence, and therefore justly paffed under the denomination of a flower. But, when, in the further progress of its decay, it crumbled into earth, it was corrupted; it loft the fpecific Effence, or fubftantial form of the flower, and affumed that of the earth, and therefore juftly changed its denomination.

The fpecific Effence, or univerfal nature that was lodged in each particular clafs of bodies, was not itself the object of any of our fenfes, but could be perceived only by the understanding. It was by the fenfible qualities, however, that we judged of the specific Effence of each object. Some of these fenfible qualities, therefore, we regarded as effential, or fuch as fhowed, by their prefence or abfence, the prefence or absence of that effential form from which they neceffarily flowed: Others were accidental, or fuch whofe prefence or abfence had no fuch neceffary confequences. The first of these two forts of qualities was called Properties; the fecond, Accidents.

In

In the Specific Effence of each object itself, they diftinguishnd two parts; one of which was peculiar and characteristical of the clafs of things of which that particular object was an individual, the other was common to it with fome other higher claffes of things. Thefe two parts were, to the Specific Effence, pretty much what the Matter and the Specific Effence were to each individual body. The one, which was called the Genus, was modified and determined by the other, which was called the Specific Difference, pretty much in the fame manner as the universal matter contained in each body was modified and determined by the Specific Effence of that particular clafs of bodies. Thefe four, with the Specific Effence or Species itself, made up the number of the Five Univerfals, fo well known in the schools by the names of Genus, Species, Differentia, Proprium, and Accidens.

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