What has been called the _Principle of Sufficient Reason_ a.s.serts, when applied to reality, that every existing reality must have a sufficient reason for existing and for being what it is.(439) Unlike the _Principle of Causality_ which is an axiomatic or self-evident truth, this principle is rather a necessary postulate of all knowledge, an a.s.sumption that _reality is intelligible_. It does not mean that all reality, or even any single finite reality, is adequately intelligible to our finite minds. In the words of Bossuet, we do not know everything about anything: "nous ne savons le tout de rien".
In regard to contingent _essences_, if these be composite we can find a sufficient reason why they are such in their const.i.tutive principles; but in regard to simple essences, or to the simple const.i.tutive principles of composite essences, we can find no sufficient reason why they are such in anything even logically distinct from themselves: they are what they are because they are what they are, and to demand why they are what they are, is, as Aristotle remarked, to ask an idle question. At the same time, when we have convinced ourselves that their actual existence involves the existence of a Supreme, Self-Existent, Intelligent Being, we can see that the essence of this Being is the ultimate ground of the intrinsic possibility of all finite essences (20).
In regard to contingent _existences_ the Principle of Sufficient Reason is coincident with the Principle of Causality, inasmuch as the sufficient reason of the actual existence of any contingent thing consists in the extrinsic real principles which are its causes. The existence of contingent things involves the existence of a Necessary Being. We may say that the sufficient reason for the existence of the Necessary Being is the Divine Essence Itself; but this is merely denying that there is outside this Being any sufficient reason, _i.e._ any cause of the latter"s existence; it is the recognition that the Principle of Causality is inapplicable to the Necessary Being. The Principle of Sufficient Reason, in this application of it, is logically posterior to the Principle of Causality.(440)
95. CLa.s.sIFICATION OF CAUSES: ARISTOTLE"S FOURFOLD DIVISION.-In modern times many scientists and philosophers have thought it possible to explain the order and course of nature, the whole cosmic process and the entire universe of our experience, by an appeal to the operation of _efficient causes_. Espousing a mechanical, as opposed to a teleological, conception of the universe, they have denied or ignored all influence of _purpose_, and eschewed all study of _final causes_. Furthermore, misconceiving or neglecting the category of substance, and the doctrine of substantial change, they find no place in their speculations for any consideration of _formal_ and _material_ causes. Yet without final, formal and material causes, so fully a.n.a.lysed by Aristotle(441) and the scholastics, no satisfactory explanation of the world of our experience can possibly be found. Let us therefore commence by outlining the traditional fourfold division of causes.
We have seen already that change involves composition or compositeness in the thing that is subject to change. Hence two _intrinsic_ principles contribute to the const.i.tution of such a thing, the one a pa.s.sive, determinable principle, its _material cause_, the other an active, determining principle, its _formal cause_. Some changes in material things are superficial, not reaching to the substance itself of the thing; these are _accidental_, involving the union of some _accidental_ "form" with the concrete pre-existing substance as material (_materia_ "_secunda_").
Others are more profound, changes of the substance itself; these are _substantial_, involving the union of a new _substantial_ "form" with the primal material princ.i.p.al (_materia_ "_prima_") of the substance undergoing the change. But whether the change be substantial or accidental we can always distinguish in the resulting composite thing two intrinsic const.i.tutive principles, its _formal cause_ and its _material cause_. The agencies in nature which, by their activity, bring about change, are _efficient causes_. Finally, since it is an undeniable fact that there is _order_ in the universe, that its processes give evidence of _regularity_, of operation according to _law_, that the cosmos reveals a _harmonious co-ordination of manifold_ agencies and a _subordination of means to ends_, it follows that there must be working in and through all nature a directive principle, a principle of plan or design, a principle according to which those manifold agencies work together in fulfilment of a purpose, _for the attainment of ends_. Hence the reality of a fourth cla.s.s of causes, _final causes_.
The separate influence of each of those four kinds of cause can be clearly ill.u.s.trated by reference to the production of any work of art. When, for instance, a sculptor chisels a statue from a block of marble, the latter is the material cause (_materia secunda_) of the statue, the form which he induces on it by his labour is the formal cause (_forma accidentalis_), the sculptor himself as agent is the efficient cause, and the motive from which he works-money fame, esthetic pleasure, etc.-is the final cause.
The formal and material causes are _intrinsic_ to the effect; they const.i.tute the effect _in facto esse_, the distinction of each from the latter being an inadequate real distinction. It is not so usual nowadays to call these intrinsic const.i.tutive principles of things _causes_ of the latter; but they verify the general definition of cause. The other two causes, the efficient and the final, are _extrinsic_ to the effect, and really and adequately distinct from it,(442) extrinsic principles of its production, its _fieri_.
This cla.s.sification of causes is adequate;(443) it answers all the questions that can be asked in explanation of the production of any effect: _a quo?_ _ex quo?_ _per quid?_ _propter quid?_ Nor is there any sort of cause which cannot be brought under some one or other of those four heads. What is called an "exemplar cause," _causa exemplaris_, _i.e._ the ideal or model or plan in the mind of an intelligent agent, according to which he aims and strives to execute his work, may be regarded as an extrinsic formal cause; or again, in so far as it aids and equips the agent for his task, an efficient cause; or, again, in so far as it represents a good to be realized, a final cause.(444)
The objects of our knowledge are in a true sense causes of our knowledge: any such object may be regarded as an efficient cause, both physical and moral, of this knowledge, in so far as by its action on our minds it determines the activity of our cognitive faculties; or, again, as a final cause, inasmuch as it is the end and aim of the knowledge.
The essence of the soul is, as we have seen (69), not exactly an efficient cause of the faculties which are its properties; but it is their final cause, inasmuch as their _raison d"etre_ is to perfect it; and their subjective or material cause, inasmuch as it is the seat and support of these faculties.
The fourfold division is a.n.a.logical, not univocal: though the matter, the form, the agent, and the end or purpose, all contribute positively to the production of the effect, it is clear that the character of the causal influence is widely different in each case.
Again, its members do not demand distinct subjects: all four cla.s.ses of cause may be verified in the same subject. For instance, the human soul is a formal cause in regard to the composite human individual, a material cause in regard to its habits, an efficient cause in regard to its acts, and a final cause in regard to its faculties.
Furthermore, the fourfold division is not an immediate division, for it follows the division of cause in general into _intrinsic_ and _extrinsic_ causes. Finally, it is a division of the causes which we find to be operative _in_ the universe. But the philosophical study of the universe will lead us gradually to the conviction that itself and all the causes in it are themselves _contingent_, themselves caused by and dependent on, a Cause _outside_ or extrinsic to the universe, a _First_, _Uncaused_, _Uncreated_, _Self-Existent_, _Necessary Cause_ (_Causa Prima_, _Increata_), at once the _efficient_ and _final_ cause of all things. In contrast with this _Uncreated_, _First Cause_, all the other causes we have now to investigate are called _created_ or _second_ causes (_causae secundae_, _creatae_).
A cause may be either _total_, _adequate_, or _partial_, _inadequate_, according as the effect is due to its influence solely, or to its influence in conjunction with, or dependence on, the influence of some other cause or causes _of the same order_. A created cause, therefore, is a total cause if the effect is due to its influence independently of other created causes; though of course all created causes are dependent, both as to their existence and as to their causality, on the influence of the First Cause. Without the activity of created efficient and final causes the First Cause can accomplish directly whatever these can accomplish-except their very causality itself, which cannot be actualized without them, but for which He can supply _eminenter_. Similarly, while it is incompatible with His Infinite Perfection that He discharge the function of material or formal cause of finite composite things, He can immediately create these latter by the simultaneous production (_ex nihilo_) and union of their material and formal principles.
A cause is said to be _in actu secundo_ when it is actually exercising its causal influence. Antecedently to such exercise, at least _prioritate naturae_, it is said to be _in actu primo_: when it has the expedite power to discharge its function as cause it is _in actu primo proximo_, while if its power is in any way incomplete, hampered or unready, it is _in actu primo remoto_.
Many other divisions of cause, subordinate to the Aristotelian division, will be explained in connexion with the members of this latter.
96. MATERIAL AND FORMAL CAUSES.-These are properly subject-matter for _Cosmology_. We will therefore very briefly supplement what has been said already concerning them in connexion with the doctrine of _Change_ (ch.
ii.). By a material cause we mean _that out of which anything is made_: _id ex quo aliquid fit_. Matter is correlative with form: from the union of these there results a composite reality endowed with either essential or accidental unity-with the former if the material principle be absolutely indeterminate and the correlative form substantial, with the latter if the material principle be some actually existing individual reality and the form some supervening accident. Properly speaking only corporeal substances have material causes,(445) but the term "material cause" is used in an extended sense to signify any potential, pa.s.sive, receptive subject of formative or actuating principles: thus the soul is the subjective or material cause of its faculties and habits; essence of existence; _genus of differentia_, etc.
In what does the positive causal influence of a material cause consist?
How does it contribute positively to the actualization of the composite reality of which it is the material cause? It _receives_ and _unites with_ the form which is educed from its potentiality by the action of efficient causes, and thus contributes to the generation of the concrete, composite individual reality.(446)
It is by reason of the causality of the _formal cause_ that we speak of a thing being _formally_ such or such. As correlative of material cause it finds its proper application in reference to the const.i.tution of corporeal things. The formative principle, called _forma substantialis_, which actuates, determines, specifies the material principle, and by union with the latter const.i.tutes an individual corporeal substance of a definite kind, is the (substantial) formal cause of this composite substance.(447) The material principle of corporeal things is of itself indifferent to any species of body; it is the form that removes this indefiniteness and determines the matter, by its union with the latter, to const.i.tute a definite type of corporeal substance.(448) The existence of different species of living organisms and different types of inorganic matter in the universe implies in the const.i.tution of these things a common material principle, _materia prima_, and a multiplicity of differentiating, specifying, formative principles, _formae substantiales_. That the distinction between these two principles in the const.i.tution of any individual corporeal substance, whether living or inorganic, is not merely a virtual distinction between metaphysical (generic and specific) grades of being in the individual, but a real distinction between separable ent.i.ties, is a scholastic thesis established in the Special Metaphysics of the organic and inorganic domains of the universe.(449)
Since the _form_ is a perfecting, actuating principle, the term is often used synonymously with _actus_, _actuality_. And since besides the essential perfection which a being has by virtue of its substantial form it may have accidental perfections by reason of supervening accidental forms, these, too, are formal causes.
In what does the causal influence of the formal cause consist? In communicating itself intrinsically to the material principle or pa.s.sive subject from whose potentiality it is evoked by the action of efficient causes; in actuating that potentiality by intrinsic union therewith, and thus determining the individual subject to be actually or formally an individual of such or such a kind.
The material and formal causes are _intrinsic_ principles of the const.i.tution of things. We next pa.s.s to an a.n.a.lysis of the two _extrinsic_ causes, and firstly of the efficient cause and its causality.
97. EFFICIENT CAUSE; TRADITIONAL CONCEPT EXPLAINED.-By efficient cause we understand that _by which_ anything takes place, happens, occurs: _id a quo aliquid fit_. The world of our external and internal experience is the scene of incessant _changes_: men and things not only are, but are constantly _becoming_. Now every such change is originated by some active principle, and this we call the efficient cause of the change. Aristotle called it t? ????t???? or ? ???? ????t???, the _kinetic_ or _moving_ principle; or again, ???? ????s??? ? eta???? ?? ?t???, _principium motus vel mutationis in alio_, "the principle of motion or change in some other thing". The result achieved by this change, the actualized potentiality, is called the _effect_; the causality itself of the efficient cause is called _action_ (p???s??), _motion_, _change_-and, from the point of view of the effect, _pa.s.sio_ (pa??s??). The perfection or endowment whereby an efficient cause acts, _i.e._ its efficiency (?????e?a), is called _active power_ (_potentia seu virtus activa_); it is also called _force_ or _potential energy_ in reference to inanimate agents, _faculty_ in reference to animate agents, especially men and animals. This active power of an efficient cause or agent is to be carefully distinguished from the _pa.s.sive potentiality_ acted upon and undergoing change. The former connotes a perfection, the latter an imperfection: _unumquodque agit inquantum est in actu, pat.i.tur vero inquantum, est in potentia_. The scope of the active power of a cause is the measure of its actuality, of its perfection in the scale of reality; while the extent of the pa.s.sive potentiality of _patiens_ is a measure of its relative imperfection. The actuation of the former is _actio_, that of the latter _pa.s.sio_. The point of ontological connexion of the two _potentiae_ is the _change_ (_motus_, ????s??), this being at once the formal perfecting of the pa.s.sive potentiality in the _patiens_ or effect, and the immediate term of the efficiency or active power of the _agens_ or cause. _Actio_ and _pa.s.sio_, therefore, are not expressions of one and the same concept; they express two distinct concepts of one and the same reality, _viz._ the change: _actio et pa.s.sio sunt idem numero motus_. This change takes place _formally_ in the subject upon which the efficient cause acts, for it is an actuation of the potentiality of the former under the influence of the latter: ? ????s?? ?? t? ????t?; ??te???e?a ??? ?st? t??t??. Considered in the potentiality of this subject-"t? t??d? ?? t?de: _hujus in hococ_"-it is called _pa.s.sio_. Considered as a term of the active power of the cause-"t??de ?p? t??de: _hujus per hoc_"-it is called _actio_.
The fact that _actio_ and _pa.s.sio_ are really and objectively one and the same _motus_ does not militate against their being regarded as two separate supreme categories, for they are objects of distinct concepts,(450) and this is sufficient to const.i.tute them distinct categories (60).
Doubts are sometimes raised, as St. Thomas remarks,(451) about the a.s.sertion that the action of an agent is not formally in the latter but in the _patiens_: _actio fit in pa.s.so_. It is clear, however, he continues, that the action is formally in the _patiens_ for it is the actuation not of any potentiality of the agent, but of the pa.s.sive potentiality of the _patiens_: it is in the latter that the _motus_ or change, which is both _actio_ and _pa.s.sio_, takes place, dependently of course on the influence of the agent, or efficient cause of the change. The active power of an efficient cause is an index of the latter"s actuality; the exercise of this power (_i.e._ _action_) does not formally perfect the agent, for it is not an actuation of any pa.s.sive potentiality of the latter; it formally perfects the _patiens_. Only _immanent_ action perfects the agent, and then not as agent but as _patiens_ or receiver of the actuality effected by the action (_cf._ 103 _infra_).
We may, then, define efficient cause as _the extrinsic principle of the change or production of anything by means of action_: _principium extrinsic.u.m a quo fluit motus vel productio rei mediante actione_.
It is a "first" principle as compared with material and formal causes for its influence is obviously prior in nature to theirs; also as compared with the other extrinsic cause, the final cause, _in ordine executionis_, not, however, _in ordine intentionis_. The "end," not as realized but as realizable, not in execution but in intention, discharges its function and exerts its influence as "final _cause_" and in this order the final cause, as will appear later, is _the first of all causes_: _finis est ultimus in executione sed primus in intentione_.
"Change or production," in the definition, is to be understood not in the strict sense in which it presupposes an existing subject or material, but in the wide sense in which it includes any production of new reality, even creation or production _ex nihilo_.
"Action," too, is to be understood in the wide sense in which it includes the action of the First Cause, which action is really identical with the essence of the latter. We conceive creation after the a.n.a.logy of the efficient action of created or "second" causes: we have no _proper_ concept of the infinite perfection of the Divine activity. In all created efficient causes not only is the action itself, but also the efficiency, force, power, faculty, which is its _proximate_ principle, really distinct from the nature or essence of the agent; the former is a substance, the latter an accident.
Finally, the action of a created efficient cause is either transitive (_transiens_) or immanent (_immanens_) according as the change wrought by the action takes place in something else (as when _the sun_ heats or lights _the earth_) or in the cause itself (as when a man reasons or wills). In the former case the action perfects not the agent but the other thing, the _patiens_; in the latter case it perfects the agent itself, _agens_ and _patiens_ being here the same identical concrete individual.(452)
98. SOME SCHOLIA ON CAUSATION. THE PRINCIPLE OF CAUSALITY.-Before enumerating the princ.i.p.al kinds of efficient cause, and a.n.a.lysing the nature of efficient causality, we may set down here certain self-evident axioms and aphorisms concerning causation in general. (_a_) The most important of these is the _Principle of Causality_, which has been enunciated in a variety of ways: _Whatever happens has a cause_; _Whatever begins to be has a cause_; _Whatever is contingent has a cause_; _Nothing occurs without a cause_. Not everything that begins to be has necessarily a _material_ cause, or a _formal_ cause, really distinct from itself. For instance, simple spiritual beings, like the human soul, have no material cause, nor any formal cause or const.i.tutive principle distinct from their essence. Similarly, the whole universe, having been created _ex nihilo_, had no pre-existing material cause. All the material beings, however, which are produced, generated, brought into actual existence in the course of the incessant changes which characterize the physical universe, have both material and formal causes. But the Principle of Causality refers mainly to extrinsic causes. It is commonly understood only of efficient causes; and only in regard to these is it self-evident. We shall see that as a matter of fact nothing happens without a _final_ cause: that intelligent purpose pervades reality through and through. This, however, is a conclusion, not a principle. What is really a self-evident, axiomatic, necessary principle is that _whatever happens has an_ EFFICIENT _cause_. Only the Necessary, Self-Existing, Eternal Being, has the sufficient reason of His actual existence in Himself, in His own essence.
That any being which is contingent could exist _independently of some other actual being_ as the cause of this existence; that it could have come into existence or begun to exist _from absolute nothingness, or be produced or brought into actual existence without any actual being to produce it_; or that, once existing and subject to change, it could undergo change and have its potentialities actualized _without any actual being to cause such change_ (10)-all this is positively unthinkable and absolutely repugnant to our intelligence; all this our reason peremptorily declares to be intrinsically impossible. Nor is there question of a mere psychological inconceivability, such as might be due to a long-continued custom of a.s.sociating the idea of a "beginning" with the idea of a "cause"
of this beginning-as phenomenists generally contend.(453) There is question of an impossibility which our reason categorically dictates to be a real, ontological impossibility. The Principle of Causality is therefore a necessary, _a priori_, self-evident principle.
(_b_) _Every effect must have an adequate efficient cause_, _i.e._ a cause sufficiently perfect, sufficiently high on the scale of being, to have the active power to produce the effect in question; otherwise the effect would be partially uncaused, which is impossible.
(_c_) _An effect cannot as such be actually more perfect than its adequate (created) cause_. The reason is that the effect as such is really dependent for its actuality on its adequate created cause. It derives its actuality from the latter. Now it is inconceivable that an agent could be the active, productive principle of a greater perfection, a higher grade of actuality, than itself possesses. Whatever be the nature of efficient causality, _actio_ and _pa.s.sio_ (102), or of the dependence of the produced actuality upon the active power of its adequate efficient cause (10), the reality of this dependence forbids us to think that in the natural order of efficient causation a higher grade of reality can be actualized than the agent is capable of actualizing, or that the agent can naturally actualize a higher or more perfect grade of reality than is actually its own. We must, however, bear in mind that there is question of the _adequate_ created cause of an effect; and that to account _fully_ for the actualization of any potential reality whatsoever we are forced to recognize in all causation of created efficient causes the _concursus_ of the _First Cause_.
(_d_) The actuality of the effect is in its adequate created cause or causes, _not actually and formally, but potentially_ or _virtually_. If the cause produce an effect of the same kind as itself (_causa ____univoca___), as when living organisms propagate their species, the perfection of the effect is said to be in the cause _equivalently_ (_aequivalenter_); if it produce an effect of a different kind from itself (_causa ____a.n.a.loga___), as when a sculptor makes a statue, the perfection of the effect is said to be in the cause _eminently_ (_eminenter_).
(_e_) _Omne agens agit inquantum est in actu._ The operative power of a being is in proportion to its own actual perfection: the higher an agent is on the scale of reality, or in other words the more perfect its grade of being, the higher and more perfect will be the effects achieved by the exercise of its operative powers. In fact our chief test of the perfection of any nature is a.n.a.lysis of its operations. Hence the maxim so often referred to already:-
(_f_) _Operari sequitur esse; qualis est operatio talis est natura; modus operandi sequitur modum essendi._ Operation is the key to nature; we know what any thing is by what it does.
(_g_) _Nihil agit ultra suam speciem_; or, again, _Omne agens agit simile sibi_. These are inductive generalizations gathered from experience, and have reference to the natural operation of agents, especially in the organic world. Living organisms reproduce only their own kind. Moreover, every agency in the universe has operative powers of a definite kind; acting according to its nature it produces certain effects and these only; others it cannot produce: this is, in the natural order of things, and with the natural _concursus_ of the First Cause. But created causes have a pa.s.sive _obediential capacity_ (_potentia obedientialis_) whereby their nature can be so elevated by the First Cause that they can produce, with His special, supernatural _concursus_, effects of an entirely higher order than those within the ambit of their natural powers.(454)
(_h_) From a known effect, of whatsoever kind, we can argue with certainty, _a posteriori_, to the _existence_ of an adequate efficient cause, and to _some knowledge_ of the _nature_ of such a cause.(455) By virtue of the principle of causality we can infer the existence of an adequate cause containing either equivalently or eminently all the perfections of the effect in question.
99. CLa.s.sIFICATION OF EFFICIENT CAUSES.-(_a_) We have already referred to the distinction between the _First_ Cause and _Second_ or _Created_ Causes. The former is absolutely independent of all other beings both as to His power and as to the exercise of this power. The latter are dependent, for both, upon the former.
The distinction between a first, or primary, or independent cause, and second, or subordinate, or dependent causes can be understood not only of causes universally, but also as obtaining among created causes themselves.
In general the _subordination_ of a cause to a superior or anterior cause may be either _essential_ or _accidental_: essential, when the second cause depends-either for its existence or for an indispensable complement of its efficiency-on the _present_ actual influence of the other cause; accidental when the second cause has indeed received its existence or efficiency from this other cause, but is now no longer dependent, for its existence or action, on the latter. Thus, living organisms are, as causes, accidentally subordinate to their parent organisms: they derived their existence from the latter, but are independent of these when in their maturity they continue to exist, and live, and act of themselves and for themselves. But all creatures, on the other hand, are, as causes, _essentially_ subordinate to the Creator, inasmuch as they can exist and act only in constant dependence on the ever present and ever actual conserving and concurring influence of the Creator.
It is obvious that all the members of any series of causes _essentially_ subordinate the one to the other _must exist simultaneously_. Whether such a series could be infinite depends, therefore, on the question whether an _actually infinite mult.i.tude_ is intrinsically possible. This difficulty cannot be urged with such force against an infinite regress in causes _accidentally_ subordinate to one another; for here such a regress would not involve an actually infinite mult.i.tude of things existing simultaneously. In the case of essentially subordinate causes, moreover, the series, whatever about its infinity, must contain, or rather imply _above_ it, _one_ cause which is _first_ in the sense of being _independent_, or exempt from the subordination characteristic of all the others. And the reason is obvious: Since no one of them can exist or act except dependently on another, and this on another, and so on, it is manifest that the series cannot exist at all unless there is some one cause which, unlike all the others, exists and acts without such subordination or dependence. Hence, _in essentially subordinate causes an infinite regress is impossible_.(456) In Natural Theology these considerations are of supreme importance.
(_b_) An efficient cause may be described as _immanent_ or _transitive_ according as the term of its action remains within the cause itself, or is produced in something else. The action of the First Cause is formally immanent, being identical with the Divine Nature itself; it is virtually transitive when it is creative, or operative among creatures.
(_c_) An efficient cause is either a _princ.i.p.al_ or an _instrumental_ cause. When two causes so combine to produce an effect that one of them uses the other the former is called the princ.i.p.al and the latter the instrumental cause. Thus I am the princ.i.p.al cause of the words I am writing; my pen is the instrumental cause of them. Such an effect is always attributed to the princ.i.p.al cause, not to the instrumental. The notion of an instrument is quite a familiar notion. An instrument helps the princ.i.p.al agent to do what the latter could not otherwise do, or at least not so easily. An instrument therefore is really a cause. It contributes positively to the production of the effect. How does it do so?
By reason of its nature or structure it influences, modifies, and directs in a particular way, the efficiency of the princ.i.p.al cause. But this property of the instrumental cause comes into play only when the latter is being actually used by a princ.i.p.al cause. A pen, a saw, a hammer, a spade, have each its own instrumentality. The pen will not cut, nor the saw mould iron, nor the hammer dig, nor the spade write, for the agent that uses them. Each will produce its own kind of effect when used; but none of them will produce any effect except when used: though each has in itself permanently and inherently the power to produce its own proper effect in use.(457) We have instanced the use of _artificial_ instruments. But nature itself provides some agencies with what may be called _natural_ instruments. The _s.e.m.e.n_ whereby living organisms propagate their kind is an instance. In a less proper sense the various members of the body are called instruments of the human person as princ.i.p.al cause, "instrumenta _conjuncta_".
The notion of an instrumental cause involves then (_a_) subordination of the latter, in its instrumental activity, to a princ.i.p.al cause, (_b_) incapacity to produce the effect otherwise than by modifying and directing the influence of the princ.i.p.al cause. This property whereby the instrumental cause modifies or determines in a particular way the influence of the princ.i.p.al cause, is called by St. Thomas an _actio_ or _operatio_ of the former; the distinction between the princ.i.p.al and the instrumental cause being that whereas the former acts by virtue of a power permanently inherent in it as a natural perfection, the latter acts as an instrument only by virtue of the transient motion which it derives from the princ.i.p.al cause which utilizes it.(458)
We may, therefore, define an _instrumental_ cause as _one which, when acting as an instrument, produces the effect not by virtue of its inherent power alone, but by virtue of a power communicated to it by some princ.i.p.al cause which acts through it_. A _princ.i.p.al_ cause, on the other hand, is _one which produces its effect by virtue of an active power permanently inherent in itself_.
The designations _princ.i.p.al_ and _instrumental_ are obviously correlative.
Moreover, _all created_ causes may be called _instrumental_ in relation to the _First Cause_. For, not only are they dependent on the latter for the _conservation_ of their nature and active powers; they are also dependent, in their action, in their actual exercise of these powers, on the First Cause (for the _concursus_ of the latter).(459) Yet some created causes have these powers permanently, and can exercise them without subordination to other creatures; while others need, for the exercise of their proper functions, not only the Divine _concursus_, but also the motion of other creatures. Hence the former are rightly called _princ.i.p.al_ created causes, and the latter _instrumental_ created causes.