1 The formal cause of a thing is generally explained to be that which constitutes it what it is; thus the soul may be said to be that which changes the dust of the earth into an organized and living body; or, again, heat may be considered the cause of a hot substance being hot, or that in which its state as hot, consists. Comparing the formal cause to other so-called causes or antecedents, it is the last in the series by which a thing is brought to be, or the ultimate state of the process which intervenes between the will of the originator and its performance; at least this will convey a notion of what is meant, sufficient for the matter in hand. Thus, according to the Council of Trent, justification, the work of God, is brought into effect through a succession of the following causes: the mercy of God the efficient cause, Christ offered on the Cross the meritorious, Baptism the instrumental, and the principle of renewal in righteousness thereby communicated the formal; upon which immediately follows justification. Or again, Faith is, by various parties, considered successively as a disposing cause, the instrumental, or the formal cause of justification, thus being brought nearer and nearer to that of which it is the cause, till it (as it were) falls into and coincides with it. Hence the form is that, between which and the thing in question nothing can be interposed in our ideas; and accordingly it is sometimes really distinct from that effect, sometimes not, though it is always supposed to be distinct. Thus, to take one of the instances given, if the renovation in righteousness which follows Baptism, or the “justitia Dei qua nos justos facit,” as the Council speaks, be considered as the principle of renewal, as I have expressed it, it is the formal cause of our renewed state itself as well as of justification; and is or is not really distinct from that renewed state, according as we believe the principle of renewal to be a mere abstraction of the mind contemplating it, or a definite divine gift residing in the soul. Again: heat, the formal cause of a hot iron, is or is not really distinct from and antecedent to its being hot, according as we view caloric as an idea or as a substance. When what is considered the formal cause is a mere abstraction of the mind, then it nearly coincides with the logical differentia, or proprium, or inseparable accident. Thus whiteness is at once the form and the accident of a white wall; and animality is the form and the generic difference of man as distinguished from a vegetable.
The ordinary meaning of the word form serves to illustrate this scientific use of it. What discriminates a body from everything else is its shape; which is the development of that of which it is composed, into and unto a certain determinate lineament and structure. The Form then is some such disposition or result, constituting a thing to be what it is. For instance, the matter of a science is its objective truth, its form is that truth when it has become subjective, or knowledge, which is a sort of determinate embodying of what was till then unappropriated.
Other instances of the formal cause are as follows:—The muscles, claws, teeth, intestines, etc. of a beast of prey so intimately harmonize with each other, as forcibly to suggest the notion that they are necessary results of some one element or principle, or that there is a certain latent type on which its whole structure is formed and from which it is developed. This, if it exists, will be the formal cause of what we mean by a beast of prey.
Again:—It is often a difficult question in pathology to determine the seat of diseases. Fever, for instance, manifests itself in certain symptoms, as quickness of pulse, restlessness, etc.; and, speaking in a vague way, we might say that it consisted in those symptoms, but it is natural to investigate whether there be not some simple disarrangement of one or other organ or function or department of the animal frame, to which these symptoms may be referred. Thus insanity has been supposed to consist in,—i.e. to have for its formal cause,—a certain determination of blood to the head; gout to be an inflammation of the membrane which covers the bones, etc. etc. In like manner, it has lately been a subject of controversy in the medical world, whether the seat of disease generally, and therefore its formal cause, was to be sought in the solids or in the fluids.
Again:—If man be defined to be a rational animal, we do not gain any real and tangible account of him, nor advance in our knowledge of him; it is an ideal, not a real view of him; but if we are told that virtue is a power of ruling the passions, or that happiness, as Aristotle says, lies in action, we have brought before us, more or less clearly, how virtue or happiness come to be, or of what they are the issue; that is, we approximate to their formal cause. When Cicero suggests that “omne bonum in honestate consistit” (Tuscul. Disp. v. 42), or that “honestas” is that quality of a thing on account of which it is called good, he is assigning the formal cause of goodness.