[Footnote 19: Alongside of these dynamic theories, there are to be found mechanical ones that arose just as early and from the same source, viz., the practical _Weltanschauung_.

It is not part of our purpose to discuss them. Their first scientific expression is to be found in the doctrine of effluences and pores in Empedokles and in Atomism.]

It is evident in what light all these dynamic conceptions appear, when looked at from the standpoint of consistent extreme empiricism. These "forces," to consider here only this one of the dynamic hypotheses, help to explain nothing. The physical forces, or those which give rise to movement, are evidently not given to us as contents of sense perception, and at the most they can be deduced as non-sensuous foundations, not as contents of possible sense perception. The often and variously expressed belief that self perception reveals to us here what our senses leave hidden has proved itself to be in all its forms a delusion. The forces whose existence we a.s.sume have then an intuitable content only in so far as they get it through the uniformities present in repeated perceptions, which uniformities are to be "explained" through them. But right here their a.s.sumption proves itself to be not only superfluous but even misleading; for it makes us believe that we have offered an explanation, whereas in reality we have simply duplicated the given by means of a fiction, quite after the fashion of the Platonic doctrine of ideas. This endeavor to give the formal temporal relations between events, which we interpret as causes and effects, a dynamic real substructure, shows itself thus to be worthless in its contributions to our thought. The same holds true of every other dynamic hypothesis. The critique called forth by these contributions establishes therefore only the validity of the empiristic interpretation.

If, however, we have once come so far, we may not hold ourselves back from the final step. Empiricism has long ago taken this step, and the most consistent among its modern German representatives has aroused anew the impulses that make it necessary. Indeed, if we start from the empiristic presuppositions, we must recognize that there lies not only in the a.s.sumption of forces, but even in the habit of speaking of causes and effects, "a clear trace of fetishism." We are not then surprised when the statement is made: The natural science of the future, and accordingly science in general, will, it is to be hoped, set aside these concepts also on account of their formal obscurity. For, so it is explained, repet.i.tions of like cases in which _a_ is always connected with _b_, namely, in which like results are found under like circ.u.mstances, in short, the essence of the connection of cause and effect, exists only in the abstraction that is necessary to enable us to repicture the facts. In nature itself there are no causes and effects.

_Die Natur ist nur einmal da._

It is, again, Stuart Mill, the man of research, not the empiricist, that opposes this conclusion, and indeed opposes it in the form that Auguste Comte had given it in connection with thoughts that can be read into Hume"s doctrine. Comte"s "objection to the _word_ cause is a mere matter of nomenclature, in which, as a matter of nomenclature, I consider him to be entirely wrong.... By rejecting this form of expression, M. Comte leaves himself without any term for marking a distinction which, however incorrectly expressed, is not only real, but is one of the fundamental distinctions in science."[20]

[Footnote 20: _Logic_, bk. III, ch. v, -- 6.]

For my own part, the right seems to be on the side of Comte and his recent followers in showing the old nomenclature to be worn out, if viewed from the standpoint of empiricism. If the relation between cause and effect consists alone in the uniformity of sequence which is hypothetically warranted by experience, then it can be only misleading to employ words for the members of this purely formal relation that necessarily have a strong tang of real dynamic dependence. In fact, they give the connection in question a peculiarity that, according to consistent empiricism, it does not possess. The question at issue in the empiristically interpreted causal relation is a formal functional one, which is not essentially different, as Ernst Mach incidentally acknowledges, from the interdependence of the sides and angles of a triangle.

Here two extremes meet. Spinoza, the most consistent of the dogmatic rationalists, finds himself compelled in his formulation of the a.n.a.lytic interpretation of the causal relation handed down to him to transform it into a mathematical one. Mach, the most consistent of recent German empiricists, finds himself compelled to recognize that the empirically synthetic relation between cause and effect includes no other form of dependence than that which is present in the functional mathematical relations. (In Germany empiricism steeped in natural science has supplanted the nave materialism saturated with natural science.) That the mathematical relations must likewise be subjected to a purely empirical interpretation, which even Hume denied them, is a matter of course.

However, this agreement of two opposing views is no proof that empiricism is on the right road. The empiristic conclusions to which we have given our attention do not succeed in defining adequately the specific nature of the causal relation; on the contrary, they compel us to deny such a relation. Thus they cast aside the concept that we have endeavored to define, that is, the judgment in which we have to comprehend whatever is peculiar to the causal connection. But one does not untie a knot by denying that it exists.

It follows from this self-destruction of the empiristic causal hypothesis that an additional element of thought must be contained in the relation of cause and effect besides the elements of reproductive recognition and those of identification and discrimination, all of which are involved in the abstract comprehension of uniform sequence. The characteristics of the causal connection revealed by our previous a.n.a.lysis const.i.tute the necessary and perhaps adequate conditions for combining the several factual perceptions into the abstract registering idea of uniform sequence. We may, therefore, expect to find that the element sought for lies in the tendency to extend the demand for causal connections over the entire field of possible experience; and perhaps we may at the same time arrive at the condition which led Hume and Mill to recognize the complete universality of the causal law in spite of the exclusively empirical content that they had ascribed to it. In this further a.n.a.lysis also we have to draw from the nature of our thought itself the means of guiding our investigation.

In the first place, all thought has a formal necessity which reveals itself in the general causal law no less than in every individual thought process, that is, in every valid judgment. The meaning of this formal necessity of thought is easily determined. If we presuppose, for example, that I recognize a surface which lies before me as green, then the perception judgment, "This surface is green," that is, the apprehension of the present perceptive content in the fundamental form of discursive thought, repeats with predicative necessity that which is presented to me in the content of perception. The necessity of thought contained in this perception judgment, as _mutatis mutandis_ in every affirmative judgment meeting the logical conditions, is recognizable through the fact that the contradictory judgment, "This surface is not green," is impossible for our thought under the presupposition of the given content of perception and of our nomenclature. It contradicts itself. I can express the contradictory proposition, for instance, in order to deceive; but I cannot really pa.s.s the judgment that is contained in it. It lies in the very nature of our thought that the predicate of an a.s.sertive judgment call contain only whatever belongs as an element of some sort (characteristic, attribute, state, relation) to the subject content in the wider sense. The same formal necessity of thought, to give a further instance, is present in the thought process of mediate syllogistic predication. The conclusion follows necessarily from the premises, for example, the judgment, "All bodies are divisible," from the propositions, "All bodies are extended," and, "Whatever is extended is divisible."

These elementary remarks are not superfluous; for they make clear that the casually expressed a.s.sertion of modern natural scientific empiricism, declaring in effect that there is no such thing as necessity of thought, goes altogether too far. Such necessity can have an admissible meaning only in so far as it denotes that in predicting or recounting _the content_ of possible experience every hypothesis is possible for thought. Of course it is, but that is not the subject under discussion.

The recognition of the formal necessity of thought that must be presupposed helps us to define our present question; for it needs no proof that this formal necessity of thought, being valid for every affirmative judgment, is valid also for each particular induction, and again for the general causal law. If in the course of our perceptions we meet uniform sequences, then the judgment, "These sequences are uniform," comprehends the common content of many judgments with formal necessity of thought. Empiricism, too, does not seriously doubt that the hypothesis of a general functional, even though only temporal, relation between cause and effect is deduced as an expectation of possible experience with necessity from our real experience. It questions only the doctrine that the relation between the events regarded as cause and effect has any other than a purely empirical import. The reality of an event that is preceded and followed uniformly by no other remains for this view, as we have seen, a possibility of thought.

In opposition to empiricism, we now formulate the thesis to be established: Wherever two events _a_ and _b_ are known to follow one another uniformly and immediately, there we must require with formal necessity that some element in the preceding _a_ be thought of as fundamental, which will determine sufficiently _b_"s appearance or make that appearance necessary. The necessity of the relation between the events regarded as cause and effect is, therefore, the question at issue.

We must keep in mind from the very start that less is a.s.serted in this formulation than we are apt to read into it. It states merely that something in _a_ must be thought of as fundamental, which makes _b_ necessary. On the other hand, it says nothing as to what this fundamental something is, or how it is const.i.tuted. It leaves entirely undecided whether or not this something that our thought must necessarily postulate is a possible content of perception or can become such, accordingly whether or not it can become an object of our knowledge, or whether or not it lies beyond the bounds of all our possible experience and hence all our possible knowledge. It contains nothing whatsoever that tells us how the determination of _b_ takes place through _a_. The word "fundamental" is intended to express all this absence of determination.

Thus we hope to show a necessity of thought peculiar to the relation between cause and effect. This is the same as saying that our proof will establish the logical impossibility of the contradictory a.s.sertion; for the logical impossibility of the contradictory a.s.sertion is the only criterion of logical necessity. Thus the proof that we seek can be given only indirectly. In the course of this proof, we can disregard the immediacy of the constant sequence and confine our attention to the uniformity of the sequence, not only for the sake of brevity, but also because, as we have seen, we have the right to speak of near and remote causes. We may then proceed as follows.

If there is not something fundamental in a constant antecedent event _a_, which determines necessarily the constant subsequent appearance of one and the same _b_,--that is, if there is nothing fundamental which makes this appearance necessary,--then we must a.s.sume that also _c_ or _d_ ..., in short, any event you will, we dare not say "follows upon,"

but appears after _a_ in irregular alternation with _b_. This a.s.sumption, however, is impossible for our thought, because it is in contradiction with our experience, on the basis of which our causal thought has been developed. Therefore the a.s.sumption of a something that is fundamental in _a_, and that determines sufficiently and necessarily the appearance of _b_, is a necessity for our thought.

The a.s.sertion of this logical impossibility (_Denkunmoglichkeit_) will at once appear thoroughly paradoxical. The reader, merely recalling the results of the empiristic interpretation given above, will immediately say: "The a.s.sumption that a _b_ does not follow constantly upon an _a_, but that sometimes _b_, sometimes _c_, sometimes _d_ ... irregularly appears, is in contradiction only with all our previous experience, but it is not on this account a _logical_ impossibility. It is merely improbable." The reader will appeal especially to the discussion of Stuart Mill, already quoted, in which Mill pictures _in concreto_ such an improbable logical impossibility, and therefore at the same time establishes it in fact. Again, the reader may bring forward the words in which Helmholtz introduces intellectual beings of only two dimensions.

"By the much misused expression, "to be able to imagine to one"s self,"

or, "to think how something happens," I understand (and I do not see how anybody can understand anything else thereby without robbing the expression of all meaning) that one can picture to one"s self the series of sense impressions which one would have if such a thing actually took place in an individual case."[21]

[Footnote 21: _Vortrage und Reden_, bd. II, "uber den Ursprung und die Bedeutung der geometrischen Axiome."]

Nevertheless, pertinent as are these and similar objections, they are not able to stand the test. We ask: "Is in fact a world, or even a portion of our world, possible for thought that displays through an absolutely irregular alternation of events a chaos in the full sense; or is the attempt to picture such a chaos only a mere play of words to which not even our imagination, not to mention our thought, can give a possible meaning?"

Perhaps we shall reach a conclusion by the easiest way, if we subject Mill"s description to a test. If we reduce it to the several propositions it contains, we get the following: (1) Every one is able to picture to himself in his imagination a reality in which events follow one another without rule, that is, so that after an event _a_ now _b_ appears, now _c_, etc., in complete irregularity. (2) The idea of such a chaos accordingly contradicts neither the nature of our mind nor our experience. (3) Neither the former nor the latter gives us sufficient reason to believe that such an irregular alternation does not actually exist somewhere in the observable world. (4) If such a chaos should be presented to us as fact, that is, if we were in a position to outlive such an alternation, then the belief in the uniformity of time relations would soon cease.

Every one would subscribe to the last of these four theses, immediately upon such a chaos being admitted to be a possibility of thought; that is, he would unless he shared the rationalistic conviction that our thought const.i.tutes an activity absolutely independent of all experience. We must simply accept this conclusion on the ground of the previous discussion and of a point still to be brought forward.

If we grant this conclusion, however, then it follows, on the ground of our previous demonstration of the reproductive and recognitive, as well as thought elements involved in the uniform sequence, that the irregularity in the appearance of the events, a.s.sumed in such a chaos, can bring about an absolutely relationless alternation of impressions for the subject that we should presuppose to be doing the perceiving. If we still wish to call it perception, it would remain only a perception in which no component of its content could be related to the others, a perception, therefore, in which not even the synthesis of the several perception contents could be apprehended as such. That is, every combination of the different perception contents, by which they become components of one and the same perception, presupposes, as we have seen, those reproductive and recognitive acts in revival which are possible only where uniformities of succession (and of coexistence) exist. Again, every act of attention involved in identifying and discriminating, which likewise we have seen to be possible only if we presuppose uniformities in the given contents of perception, must necessarily disappear when we presuppose the chaotic content; and yet they remain essential to the very idea of such a chaos. A relationless chaos is after all nothing else than a system of relations thought of without relations! That the same contradiction obtains also in the mere mental picturing of a manifold of chaotic impressions needs no discussion; for the productive imagination as well as the reproductive is no less dependent than is our perceptive knowledge upon the reproductive recognition and upon the processes of identifying and discriminating.

Thus the mental image of a chaos could be formed only through an extended process of ideation, which itself presupposes as active in it all that must be denied through the very nature of the image. A relationless knowledge, a relationless abstraction, a relationless reproduction or recognition, a relationless identification or discrimination, in short, a relationless thought, are, as phrases, one and all mere contradictions. We cannot picture "through our relating thought," to use Helmholtz"s expression, nor even in our imagination, the sense impressions that we should have if our thought were relationless, that is, were nullified in its very components and presuppositions. In the case of Helmholtz"s two dimensional beings, the question at issue was not regarding the setting aside of the conditions of our thought and the subst.i.tuting conditions contradictory to them, but regarding the setting aside of a part of the content of our sense intuition, meanwhile retaining the conditions and forms peculiar to our thought. In this case, therefore, we have a permissible fiction, whereas in Mill"s chaos we have an unthinkable thought.

Again, the sense impressions that must be presupposed in an inherently relationless chaos have no possible relation to the world of our perception, whose components are universally related to each other through the uniformities of their coexistences and sequences.

Accordingly, the remark with which Helmholtz concludes the pa.s.sage above quoted holds, _mutatis mutandis_, here also. "If there is no sense impression known that stands in relation to an event which has never been observed (by us), as would be the case for us were there a motion toward a fourth dimension, and for those two dimensional beings were there a motion toward our third dimension; then it follows that such an "idea" is impossible, as much so as that a man completely blind from childhood should be able to "imagine" the colors, if we could give him too a conceptual description of them."

Hence the first of the theses in which we summed up Stuart Mill"s a.s.sumptions must be rejected. With it go also the second and third. In this case we need not answer the question: In how far do these theses correspond to Mill"s own statements regarding the absolute surety and universality of the causal law?

We have now found what we sought, in order to establish as a valid a.s.sertion the seeming paradox in the proof of the necessity that we ascribe to the relation between cause and effect. We have proved that the a.s.sumption of a completely irregular and therefore relationless alternation of impressions contradicts not only our experience, but even the conditions of our thought; for these presuppose the uniformities of the impressions, and consequently our ability to relate them, all which was eliminated from our hypothetical chaos. Hence we have also established that a necessary relation is implied in the thought of a constant sequence of events, which makes the uniformly following _b_ really dependent upon the uniformly preceding _a_.

From still another side, we can make clear the necessity a.s.serted in the relation of cause and effect. We found that the connection between each definite cause and its effect is an empirically synthetic one and has as its warrant merely experience. We saw further that the necessity inherent in the causal connection contains merely the demand that there shall be something fundamental in the constantly preceding _a_ which makes the appearance of _b_ necessary; not, however, that it informs us what this efficacy really is, and hence also not that it informs us how this efficacy brings about its effect. Finally, we had to urge that every induction, the most general no less than the most particular, depends upon the presupposition that the same causes will be given in the reality not yet observed as in that already observed. This expectation is warranted by no necessity of thought, not even by that involved in the relation of cause and effect; for this relation begins for future experience only when the presupposition that the same causes will be found in it is a.s.sumed as fulfilled.[22] This expectation is then dependent solely upon previous experience, whose servants we are, whose lords we can never be. Therefore, every induction is an hypothesis requiring the verification of a broader experience, since, in its work of widening and completing our knowledge, it leads us beyond the given experience to a possible one. In this respect we can call all inductive thought empirical, that is, thought that begins with experience, is directed to experience, and in its results is referred to experience.

The office of this progressing empirical thought is accordingly to form hypotheses from which the data of perception can be regressively deduced, and by means of which they can be exhibited as cases of known relations of our well-ordered experience, and thus can be explained.

[Footnote 22: The only empiricism which can maintain that the same causes would, in conformity with the causal law, be given in the un.o.bserved reality, is one which puts all events that can be regarded as causes in the immediately given content of perception as its members. Such a view is not to be found in Mill; and it stands so completely in the way of all further a.n.a.lysis required of us by every perception of events that no attention has been paid in the text to this extreme of extremes.]

The way of forming hypotheses can be divided logically into different sections which can readily be made clear by an example. The police magistrate finds a human corpse under circ.u.mstances that eliminate the possibility of accident, natural death, or suicide; in short, that indicate an act of violence on the part of another man. The general hypothesis that he has here to do with a crime against life forms the guide of his investigation. The result of the circ.u.mstantial evidence, which we presuppose as necessary, furnishes then a special hypothesis as following from the general hypothesis.

It is clear that this division holds for all cases of forming hypotheses. A general hypothesis serves every special hypothesis as a heuristic principle. In the former we comprehend the causal explanation indicated immediately by the facts revealed to our perception in the special case. It contains, as we might also express it, the genus to the specific limitations of the more exact investigation. But each of these general hypotheses is a modification of the most general form of building hypotheses, which we have already come to know as the condition of the validity of all inductive inferences, that is, as the condition for the necessity of their deduction, and, consequently, as the condition for the thought that like causes will be given in the reality not yet observed as in that already observed. We have further noticed that in this most general form of building hypotheses there lie two distinct and different valid a.s.sumptions: beside the empirical statement that like causes will be given, which gives the inductive conclusion the hypothetical form, there stands the judgment that like causes bring forth like effects, a corollary of the causal law. The real dependence of the effect upon the cause, presupposed by this second proposition and the underlying causal law, is not, as was the other a.s.sumption, an hypothesis, but a necessary requirement or _postulate_ of our thought.

Its necessity arises out of our thought, because our experience reveals uniformity in the sequence of events. From this point of view, therefore, the causal law appears as a postulate of our thought, grounded upon the uniformity in the sequence of events. It underlies every special case of constructing hypotheses as well as the expectation that like causes will be given in the reality not yet observed.

Mill"s logic of induction contains the same fault as that already present in Hume"s psychological theory of cause. Hume makes merely the causal law itself responsible for our inductive inferences, and accordingly (as Mill likewise wrongly a.s.sumes) for our inferences in general. But we recognize how rightly Mill came to a.s.sert, in contradiction to his empiristic presuppositions, that the causal law offers "an undoubted a.s.surance of an invariable, universal, and unconditional," that is, necessary, sequence of events, from which no seeming irregularity of occurrence and no gap in our experience can lead us astray, as long as experience offers uniformities of sequence.

Rationalism is thus in the right, when it regards the necessary connection as an essential characteristic of the relation between cause and effect, that is, recognizes in it a relation of real dependence. At this point Kant and Schopenhauer have had a profounder insight than Hume and Stuart Mill. Especially am I glad to be in agreement with Lotze on a point which he reached by a different route and from essentially different presuppositions. Lotze distinguishes in pure logic between postulates, hypotheses, and fictions. He does not refer the term "postulate" exclusively to the causal law which governs our entire empirical thought in its formation of hypotheses, but gives the term a wider meaning. "Postulates" are only corollaries from the inductive fundamental form of all hypothesis construction, and correspond essentially to what we have called general or heuristic hypotheses. His determination of the validity of these postulates, however, implies the position to be a.s.signed to the causal law and therefore not to those heuristic hypotheses. "The postulate is not an a.s.sumption that we can make or refrain from making, or, again, in whose place we can subst.i.tute another. It is rather an (absolutely) necessary a.s.sumption without which the content of the view at issue would contradict the laws of our thought."[23]

[Footnote 23: _Logic_, 1874, buch II, kap. viii.]

Still the decision that we have reached is not on this account in favor of rationalism, as this is represented for instance by Kant and his successors down to our own time, and professed by Lotze in the pa.s.sage quoted, when he speaks of an absolute necessity for thought. We found that the causal law requires a necessary connection between events given us in constant sequence. It is not, however, on that account a law of our thought or of a "pure understanding" which would be absolutely independent of all experience. When we take into consideration the evolution of the organic world of which we are members, then we must say that our intellect, that is, our ideation and with it our sense perception, has evolved in us in accordance with the influences to which we have been subjected. The common elements in the different contents of perception which have arisen out of other psychical elements, seemingly first in the brute world, are not only an occasion, but also an efficient cause, for the evolution of our processes of reproduction, in which our memory and imagination as well as our knowledge and thought, psychologically considered, come to pa.s.s. The causal law, which the critical a.n.a.lysis of the material scientific methods shows to be a fundamental condition of empirical thought, in its requirement that the events stand as causes and effects in necessary connection, or real dependence, comprehends these uniform contents of perception only in the way peculiar to our thought.

Doubtless our thought gives a connection to experience through this its requirement which experience of itself could not offer. The necessary connection of effect with cause, or the real dependence of the former upon the latter, is not a component of possible perception. This requirement of our thought does not, however, become thereby independent of the perceptive elements in the presuppositions involved in the uniformity of sequence. The _a priori_ in the sense of "innate ideas,"

denoting either these themselves or an absolutely _a priori_ conformity to law that underlies them, for instance, our "spontaneity," presupposes in principle that our "soul" is an independently existing substance in the traditional metaphysical sense down to the time of Locke. Kant"s rationalistic successors, for the most part, lost sight of the fact that Kant had retained these old metaphysical a.s.sumptions in his interpretation of the transcendental conditions of empirical interaction and in his cosmological doctrine of freedom. The common root of the sensibility and of the understanding as the higher faculty of knowledge remains for Kant the substantial force of the soul, which expresses itself (just as in Leibnitz) as _vis pa.s.siva_ and _vis activa_. The modern doctrine of evolution has entirely removed the foundation from this rationalism which had been undermined ever since Locke"s criticism of the traditional concept of substance.

To refer again briefly to a second point in which the foregoing results differ from the Kantian rationalism as well as from empiricism since Hume: The postulate of a necessary connection between cause and effect, as we have seen, in no way implies the consequence that the several inductions lose the character of hypotheses. This does not follow merely from the fact that all inductions besides the causal law include the hypothetical thought that the same causes will be given in the reality not yet observed as appear in that already observed. The hypothetical character of all inductive inferences is rather revealed through the circ.u.mstance that in the causal postulate absolutely nothing is contained regarding _what_ the efficacy in the causes is, and _how_ this efficacy arises.

Only such consequences of the foregoing interpretation of the causal law and of its position as one of the bases of all scientific construction of hypotheses may be pointed out, in conclusion, as will help to make easier the understanding of the interpretation itself.

The requirement of a necessary connection, or dependence, is added by our thought to the reproductive and recognitive presuppositions that are contained in the uniformity of the sequence of events. If this necessary connection be taken objectively, then it reveals as its correlate the requirement of a real dependence of effect upon cause. We come not only upon often and variously used rationalistic thoughts, but also upon old and unchangeable components of all empirical scientific thought, when we give the name "force" to the efficacy that underlies causes. The old postulate of a dynamic intermediary between the events that follow one another constantly retains for us, therefore, its proper meaning. We admit without hesitation that the word "force" suggests fetishism more than do the words "cause" and "effect;" but we do not see how this can to any degree be used as a counter-argument. All words that were coined in the olden time to express thoughts of the practical _Weltanschauung_ have an archaic tang. Likewise all of our science and the greater part of our nomenclature have arisen out of the sphere of thought contained in the practical _Weltanschauung_, which centred early in fetishism and related thoughts. If, then, we try to free our scientific terminology from such words, we must seek refuge in the Utopia of a _lingua universalis_, in short, we must endeavor to speak a language which would make science a secret of the few. Or will any one seriously maintain that a thought which belongs to an ancient sphere of mental life must be false for the very reason that it is ancient?

In any case, it is fitting that we define more closely the sense in which we are to regard forces as the dynamic intermediaries of uniform occurrence. Force cannot be given as a content of perception either through our senses or through our consciousness of self; in the case of the former, not in our kinesthetic sensations, in the case of the latter, not in our consciousness of volition. Volition would not include a consciousness of force, even though we were justified in regarding it as a simple primitive psychosis, and were not compelled rather to regard it as an intricate collection of feelings and sensations as far as these elementary forms of consciousness are connected in thought with the phenomena of reaction. Again, forces cannot be taken as objects that are derived as _possible_ perceptions or after the a.n.a.logy of possible perceptions. The postulate of our thought through which these forces are derived from the facts of the uniform sequence of events, reveals them as limiting notions (_Grenzbegriffe_), as specializations of the necessary connection between cause and effect, or of the real dependence of the former upon the latter; for the manner of their causal intermediation is in no way given, rather they can be thought of only as underlying our perceptions. They are then in fact _qualitates occultae_; but they are such only because the concept of quality is taken from the contents of our sense and self perception, which of course do not contain the necessary connection required by our thought. Whoever, therefore, requires from the introduction of forces new contents of perception, for instance, new and fuller mechanical pictures, expects the impossible.

The contempt with which the a.s.sumption of forces meets, on the part of those who make this demand, is accordingly easily understood, and still more easily is it understood, if one takes into consideration what confusion of concepts has arisen through the use of the term "force" and what obstacles the a.s.sumption of forces has put in the way of the material sciences. It must be frankly admitted that this concept delayed for centuries both in the natural and moral sciences the necessary a.n.a.lysis of the complicated phenomena forming our data. Under the influence of the "concept philosophy" it caused, over and over again, the setting aside of the problems of this a.n.a.lytical empirical thought as soon as their solution had been begun. This misuse cannot but make suspicious from the very start every new form of maintaining that forces underlie causation.

However, misuse proves as little here against a proper use as it does in other cases. Moreover, the scruples that we found arising from the standpoint of empiricism against the a.s.sumption of forces are not to the point. In a.s.suming a dynamic intermediary between cause and effect, we are not doubling the problems whose solution is inc.u.mbent upon the sciences of facts, and still less is it true that our a.s.sumption must lead to a logical circle. That is, a comparison with the ideas of the old concept philosophy, which even in the Aristotelian doctrine contain such a duplication, is not to the point. Those ideas are hypostasized abstractions which are taken from the uniformly coexisting characteristics of objects. Forces, on the other hand, are the imperceivable relations of dependence which we must presuppose between events that follow one another uniformly, if the uniformity of this sequence is to become for us either thinkable or conceivable. The problems of material scientific research are not doubled by this presupposition of a real dynamic dependence, because it introduces an element not contained in the data of perception which give these problems their point of departure. This presupposition does not renew the thought of an a.n.a.lytic rational connection between cause and effect which the concept philosophy involves; on the contrary, it remains true to the principle made practical by Hume and Kant, that the real connection between causes and their effects is determinable only through experience, that is, empirically and synthetically through the actual indication of the events of uniform sequence. How these forces are const.i.tuted and work, we cannot know, since our knowledge is confined to the material of perception from which as a basis presentation has developed into thought. The insight that we have won from the limiting notion of force helps us rather to avoid the misuse which has been made of the concept of force. A fatal circle first arises, when we use the unknowable forces and not the knowable events for the purpose of explanation, that is, when we cut off short the empirical a.n.a.lysis which leads _ad infinitum_. To explain does not mean to deduce the known from the unknown, but the particular from the general. It was therefore no arbitrary judgment, but an impulse conditioned by the very nature of our experience and of our thought, that made man early regard the causal connection as a dynamic one, even though his conception was of course indistinct and mixed with confusing additions.

The concept of force remains indispensable also for natural scientific thought. It is involved with the causal law in every attempt to form an hypothesis, and accordingly it is already present in every description of facts which goes by means of memory or abstraction beyond the immediately given content of present perception. In introducing it we have in mind, moreover, that the foundations of every possible interpretation of nature possess a dynamic character, just because all empirical thought, in this field as well, is subordinate to the causal law. This must be admitted by any one who a.s.sumes as indispensable aids of natural science the mechanical figures through which we reduce the events of sense perception to the motion of ma.s.s particles, that is, through which we a.s.sociate these events with the elements of our visual and tactual perception. All formulations of the concept of ma.s.s, even when they are made so formal as in the definition given by Heinrich Hertz, indicate dynamic interpretations. Whether the impelling forces are to be thought of in particular as forces acting at a distance or as forces acting through collision depends upon the answer to the question whether we have to a.s.sume the dynamic ma.s.s particles as filling s.p.a.ce discontinuously or continuously. The dynamic basis of our interpretation of nature will be seen at once by any one who is of the opinion that we can make the connection of events intelligible without the aid of mechanical figures, for instance, in terms of energy.

Thus it results that we interpret the events following one another immediately and uniformly as causes and effects, by presupposing as fundamental to them forces that are the necessary means of their uniformity of connection. What we call "laws" are the judgments in which we formulate these causal connections.

A second and a third consequence need only be mentioned here. The hypothesis that interprets the mutual connection of psychical and physical vital phenomena as causal one is as old as it is natural. It is natural, because even simple observations a.s.sure us that the mental content of perception _follows_ uniformly the instigating physical stimulus and the muscular movement the instigating mental content which we apprehend as will. We know, however, that the physical events which, in raising the biological problem, we have to set beside the psychical, do not take place in the periphery of our nervous system and in our muscles, but in the central nervous system. But we must a.s.sume, in accordance with all the psycho-physiological data which at the present time are at our disposal, that these events in our central nervous system do not follow the corresponding psychical events, but that both series have their course simultaneously. We have here, therefore, instead of the real relation of dependence involved in constant sequence, a real dependence of the simultaneity or correlative series of events. This would not, of course, as should be at once remarked, tell as such against a causal connection between the two separate causal series. But the contested parallelistic interpretation of this dependence is made far more probable through other grounds. These are in part corollaries of the law of the conservation of energy, rightly interpreted, and in part epistemological considerations. Still it is not advisable to burden methodological study, for instance, the theory of induction, with these remote problems; and on that account it is better for our present investigation to subordinate the psychological interdependences, to the causal ones in the narrower sense.