PROLOGUE

             When several things are ordained to a single thing, one of them must rule or govern and the rest be ruled or governed, as the Philosopher teaches in the Politics. This indeed is evident in the union of soul and body, for the soul naturally commands and the body obeys. The same thing is also true of the soul's powers, for the concupiscible and irascible appetites are ruled in a natural order by reason. Now all the sciences and arts are ordained to a single thing, namely, to man's perfection, which is happiness. Hence one of these sciences and arts must be the mistress of all the others, and this one rightly lays claim to the name wisdom; for it is the office of the wise man to direct others.

             We can discover which science this is and the sort of things with which it is concerned by carefully examining the qualities of a good ruler; for just as men of superior intelligence are naturally the rulers and masters of others, whereas those of great physical strength and little intelligence are naturally slaves, as the Philosopher says in the aforementioned book, in a similar way that science which is intellectual in the highest degree should be naturally the ruler of the others. This science is the one which treats of the most intelligible objects.

             Now the phrase "most intelligible objects" can be understood in three ways. First, from the viewpoint of the order of knowing; for those things from which the intellect derives certitude seem to be more intelligible. Therefore, since the certitude of science is acquired by the intellect knowing causes, a knowledge of causes seems to be intellectual in the highest degree. Hence that science which considers first causes also seems to be the ruler of the others in the highest degree.

             Second, this phrase can be understood by comparing the intellect with the senses; for while sensory perception is a knowledge of particulars, the intellect seems to differ from sense by reason of the fact that it comprehends universals. Hence that science is pre-eminently intellectual which deals with the most universal principles. These principles are being and those things which naturally accompany being, such as unity and plurality, potency and act. Now such principles should not remain entirely undetermined, since without them a complete knowledge of the principles which are proper to any genus or species cannot be had. Nor again should they be dealt with in any one particular science; for, since a knowledge of each class of beings stands in need of these principles, they would with equal reason be investigated in every particular science. It follows, then, that such principles are treated by one common science, which, since it is intellectual in the highest degree, is the mistress of the others.

             Third, this phrase can be understood from the viewpoint of the intellect's own knowledge. For since each thing has intellective power by virtue of being free from matter, those things must be intelligible in the highest degree which are altogether separate from matter. For the intelligible object and the intellect must be proportionate to each other and must belong to one and the same genus, since the intellect and the intelligible object are one in actuality. Now those things are separate from matter in the highest degree which abstract not only from designated matter, "as the natural forms taken universally, of which the philosophy of nature (scientia naturalis treats," but from sensible matter altogether; and these are separate from matter not only in their intelligible constitution (ratio), as the objects of mathematics, but also in being, as God and the intelligences. Therefore the science which considers such things seems to be the most intellectual and the ruler or mistress of the others.

             Now this threefold consideration should be assigned to one and the same science and not to different sciences. For the separate substances mentioned above are the universal and first causes of being. Moreover, it pertains to one and the same science to consider both the proper causes of some genus and the genus itself; for example, the philosophy of nature considers the principles of a natural body. Consequently it must be the office of one and the same science to consider separate substances and being in general (ens commune), which is the genus of which the substances mentioned above are the common and universal causes.

             From this it is evident that, although this science [i.e., metaphysics or first philosophy] studies the three classes of things mentioned above, it does not investigate any one of them as its subject, but only being in general. For the subject of a science is the genus whose causes and properties we seek, and not the causes themselves of the particular genus studied, because a knowledge of the causes of some genus is the goal to which the investigation of a science attains. Now although the subject of this science is being in general, the whole of it is predicated of those things which are separate from matter both in their intelligible constitution and in being (esse). For it is not only those things which can never exist in matter which are said to be separate from matter in their intelligible constitution and in being, such as God and the intellectual substances, but also those things which can exist without matter, such as being in general. This could not be the case, however, if their being depended on matter.

             Therefore in accordance with the three classes of objects mentioned above from which this science derives its perfection, three names arise. It is called divine science or theology inasmuch as it considers the aforementioned substances. It is called metaphysics inasmuch as it considers being and the attributes which naturally accompany being (for things which transcend the physical order are discovered by the process of analysis, as the more common are discovered after the less common). And it is called first philosophy inasmuch as it considers the first causes of things. Therefore it is evident what the subject of this science is, and how it is related to the other sciences, and by what names it is designated.