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jects, which we must here point out. There are certain | This is the most immediately ascertained class of t kinds of objects that agree with one another, and differ universe of things coming under our cognisance. from all other things in a great and unknown number 2d, The minds themselves which experience titre of attributes; so that their agreement with one another feelings. We require to distinguish the mind frsto its is very intimate, and their distinction from all other susceptibilities, and to define it as the thing in which things very wide. Thus if we take human beings, we all these reside. find that they have an exceedingly large and complex 3d, The bodies or external objects that are the cause agreement, or they possess more features in common of those feelings, or states, or consciousness, and all the than we can enumerate, or than we may ever be able, special powers or distinguishable properties of these after all our study of the human subject, to reckon up; bodies. We have already explained that it has pleased for to know them all would be to attain the perfect Nature to provide substances which have a manifod knowledge of man. It is the same with many classes effect upon the human susceptibilities, leading to disof animals. If we take the dog, we find that there is tinct conceptions, and the imposition of separate names an almost inexhaustible fund of common features which for the various powers or properties thus made knopa. mark the dog as a kind apart from all other animals The world of outward objects - these objects berg and things. So iron, silver, phosphorus, are of this taken as wholes, and also as possessing each a nune description: the specimens of any one agree with one rous assemblage of powers, which must be named and another in all the properties discovered and undisco- described, as well as the total masses—makes one large vered that attach to that one; the entire discovery of class of our nameable and knowable things, and us all these properties being the perfect knowledge of the such must be recognised in Logic. We can only be species. Such objects are called 'lowest species,' or aware of these by their action on our minds; and hence
lowest kinds,' because they cannot be subdivided into it is necessary to class them subsequently to the states others, having the same totality of differences from one of consciousness or feelings which make them know, another. Thus if we divide man into white, red, tawny, and which alone are properly present to the mind. The and black races, these cannot be called species in con- external universe does not require for our present par. sequence of these distinctions alone: if all the difference pose to be more minutely classified; the chief point ? between one race and another can be expressed in one garding it being the point now stated as to the comples single attribute, such as colour, or in two or three de- power of its individual objects upon the mind, upon finite attributes, then these races are not different in which the whole of the abstractive process is founded. kind, they are not specifically, or in toto distinguished; 4th, The Successions and Co-existences, the Likethe subdivided classes are called varieties, and not nesses and Unlikenesses, between feelings or states of kinds. But if it were discovered that an indefinite and consciousness, and between the outward objects that unknown number of properties distinguished a Negro produce them. In addition to the individual feeling from a European, as in the case of a man and a of the mind, and the individual objects of the world, monkey, or a dog and a horse, European and Negro we are led to take notice of their positions, movements, would be different kinds. The classes that are not and similarities, or want of similarity. If thought and separate kinds may be exemplified by solids, liquids, nature were dead and still, there would be nothing to and gases, of the same substance; for these differ only mark but position; but as both are incessantly moving by a limited and assignable difference, all traceable to and changing, we must take cognisance of the more the one agency of heat. So houses, lands, rivers, are ments, and see how one thing follows another. If no true classes, but they are not true kinds; for the ex- two things were ever alike, perception of Likeness tent of their agreement with one another, and of their would be impossible; but as the world has been cod. difference from other things, is limited and assignable; stituted on the principle of repeating the same objects very unlike the differences between iron and gold, which in innuinerable circumstances, the examples of this affect all the senses, and which ramify and show them- must force themselves on our attention, and we must selves in a boundless number of ways.
signify, by appropriate names or descriptions, that such All the names of kinds are nouns; and although likenesses occur, so far as we descry them. Our coadjectives and abstract terms are formed from them, it ceptions are at the mercy of the outward universe, is always a limited and imperfect derivation. Thus and ought to follow it as closely as possible; hence the adjective manly,' and the abstract noun ‘manli- our processes of naming, with the view of communicatness,' are very far from expressing all that is common ing our knowledge, ought to correspond to the same to man; they only point out some one property which common source of sensation and thought. We mus conspicuously attracts attention for some reason or therefore, in addition to feelings, objects, and their another. But the names of classes that are not kinds properties, possess a means of describing the co-existreadily take on the adjective and abstract form-as ences of these, their successions, their likeness, and un* liquid,' 'liquidity;' circle, circular,'.' circularity.' likenesses; and beyond these there is nothing that we These derivations are perfectly strict and proper; and can take a hold of. We exhaust all that passes in our it is only such names as are formed from classes, not minds, and all that we suppose to pass in nature, in kinds, or limited and ascertained in their common fea- the comprehensive grouping of Feelings, Minds, Ex: tures, that can properly yield adjectives and abstract ternal Causes of Feeling, and the Co-Existences, and nouns with a strictly logical application.
Successions, Likenesses, and Unlikeness of these Feel.
ings, and their external causes. The entire action of Nameable Things.
the universe on the mind of man presents nothing that • It is of importance, as a preliminary to explaining is not included in these four heads. the nature of affirmations or assertions, to have a general view of the things presented to us for receiving
Nature of Assertions or Propositions. names, and for becoming the subjects of such affirma- In our exposition of names, we made no reference to tions or assertions; in other words, it is convenient to matters of belief or disbelief. We spoke of objects and possess a comprehensive classification of the whole of of their properties, conjunct and single, and of the conthe things that can become part and parcel of the ceptions formed of these, and of the names and descripthoughts, conceptions, or knowledge of men. Mr John tions given of those conceptions; but a mere notion er Stuart Mill, in his great work on Logic, has devised a conception is not a matter of belief. We must now, classification of the universe of knowable and nameable however, proceed to state the nature of assertions, affirexistences as follows :
mations, or propositions, which all mean things to be 1st, Feelings, or states of consciousness, or every- believed or disbelieved, and therefore to be proved or thing which the mind is said to be aware of, or which disproved. A matter of belief means something we can produces an influence upon it. These include all sensa- act upon; something that will enable us to do one thing tions, thoughts, emotions, activities, volitions, and what- for the sake of attaining some other thing. When we ever is said to be felt or entertained by the human mind. I say bread is nourishing,' we do more than announce
an object, 'bread,' and a property, 'nourishing:' we | is situated on the Thames;!“the battle of Hastings was tie these two things together with a bond of union fought in 1066;' (the sun is in the sign Aries. And the which rouses the activity of the human mind, and assertions of the properties of things belong to the same causes it to set to work in some given course. Asser- class-as when we say 'silver is precious,' tigers are fetions are not idle notions, but things of power and rocious,''man walks upright. We have remarked that might; they are the intellectual machinery that rules nature produces objects that have a manifold action the greater part of human life. When a man feels the on the human susceptibilities; each separate action want of nourishment, and is reminded of the assertion being commonly called one of the properties of the that bread is nourishing,' he applies his active ener- entire object. Now when we assert that certain progies to procure the bread, in the full assurance that he perties of a thing accompany certain others, we make will thereby have something more than meets his eye affirmations of co-existence. *Gold does not rust,' is a in a loaf: that he will have his bodily strength re- proposition which may be interpreted to mean that a newed, and his appetite gratified. Belief is the state certain substance recognised by us as yellow, heavy, preliminary to action, or the state disposing to action and of high marketable value (the popular and obvious wben some given emergency arises; and assertions or characteristics of gold), has also the property of not propositions are what call forth this faith or belief. rusting, like iron or lead.
An assertion requires, in the first place, that there Propositions of Succession will readily occur to any should be two things mentioned: it is not possible so one. 'Night follows day;''Queen Victoria followed King to mention a single object as that it shall be a matter William IV.;' and all the affirmations of historical narof belief or disbelief. Thus 'fire burns,' 'gold is yel. ration are propositions of this kind. The distinction low, bread is nourishing,' the sun is the centre of between geography and history is a distinction between the planetary motions,' each contains at least two things the contemporaneous and the successive : the proposior notions coupled together. Fire is one thing, burning tions of geography express co-existence and order in is a different thing, if there be any meaning or anything place; those in history, succession and order in time. to believe in the assertion. But the mention of two The particular case of succession entitled Causation, things is not enough: the two names of 'gold,' .yellow is one very important in respect to the order of the colour,' do not make an assertion of themselves; the world, and to our knowledge of that order; and although asserting power is conferred by the verb “is;' and we the idea of a cause and effect is familiar and intellishall find that every assertion requires a verb, or that gible to most people, it belongs to Logic to clear it up, the verb is the part of speech which completes the force and to represent it with the utmost possible precision, of an assertion, or has the power of causing belief or 80 that there may not be any doubt hanging over it in disbelief in the human mind. The question, then, the most obscure and perplexed instances which can arises—what is the import of those verbs which are possibly occur. We shall have to take this up at an the bonds of union between the things coupled together after stage; and at present we need only remind the in assertions!
reader, that the succession of cause and effect implies a As assertions can relate only to the actual facts and fixed and invariable bond of connection, such as is appearances of the world, they must refer to some of never to be interrupted at any time, or under any cirthe great classes of things above enumerated, as consti- cumstances; we commonly recognise a sort of unfailing tuting the entire universe of the knowable. Accord - power in the cause to bring on the effect, which we may ingly, Mr Mill has shown that all possible assertions confide in to the very uttermost. may be reduced to five general heads, determined by We have compared geography with history, as exthe fourth class of nameable things, or the class com- hibiting generally the contrast of the contemporaneous prehending Successions, Co-Existences, Likenesses, and with the successive; and we may likewise compare Unlikenesses. If we add to these four things the idea natural history, which exhibits the properties conof mere Existence, we shall possess a summary of joined in the individual objects nature, with the everything that can ever come to be asserted in any sciences of physics, chemistry, &c. which are sciences affirination or proposition.
of causation, in order to contrast the contemporaneous We may, however, premise, before illustrating this things bound together by a natural and indissoluble statement of the meanings of assertions, that proposi- bond, with the successive things bound together with tions may be either affirmative or negative: they inay the same indissoluble connection. The conjunctions of either propose something for belief, or as a ground of geography (such as the Atlantic divides Europe from confidence and action; or they may propose something America, Africa is the country of the Negroes') are in for disbelief, forbidding us to accept such thing as a great part loose and casual, and so are many of the ground of action. This is the only real and permanent successions of history; but the conjunctions described distinction among propositions as to the forın of their in natural history are firm and unalterable, and be. making their assertion. Other divisions, as into simple long to the deep and fundamental collocations of creaand complex, and into categorical or unqualified, and tion; and in like manner the successions of cause and hypothetical or conditional, are not fundamental divi- effect are nature's unalterable successions. The consions. Each complex proposition may be reduced to trast between anatomy and physiology is a limited simple propositions; and the conditional or qualified example of the same distinction : the delineations of assertions may also be put in a form resembling the anatomy refer to co-existing objects, bound together by categorical or unqualified.
nature's links for connecting the properties of kinds; It may be said, then, of assertions or propositions, the laws of physiology are laws of Cause and Effect. that they affirm or deny some one or other of these The diamond is composed of carbon,' is a proposition five things—Existence, Co-Existence, Succession, Causa- of fixed natural conjunction; ‘heat liquifies solids,' is tion (a peculiar and important kind of Succession), or a proposition of fixed natural succession or causation. Resemblance. No proposition can be enunciated, no The only renaining kind of propositions are the piece of knowledge or information conveyed, nothing assertions of Likeness or Resemblance, which are totally believed or disbelieved, nothing presented as a guide distinct from assertions of contiguity either in place or to human action, that does not assert or deny of some in time; but they have the same natural basis as these thing or things one of these five attributes.
--that is, nature, besides presenting contiguities, both In the case of Existence, a single object or thing is loose and fixed, presents a copious store of siroilarities sufficient material for an assertion--as when we say, among the objects that she reveals to our knowledge. 'the sun exists,'«God is.' But in all the others, it is These similarities are usually considered to be of all obvious that there must be at least two things; for the degrees ; but, strictly speaking, this is not the case. very nature of the attributes of co-existence, succes. The idea of unequal similarity arises from the fact sion, and likeness, is to imply plurality-to co-exist, to already alluded to—that a number of natural objects succeed one another, or to resemble one another. are often found agreeing in some of their properties, Propositions of Co-Existence are such as London and not in others; and, speaking of the entire objects,
we say that they have only an imperfect or partial | ceived in general, that mankind could not be mistaken similarity. The most perfect similarity is what is in any conception made up of them. called Identity – that is, taking the same object at For the sake of accurate reasoning, every general different times, no change having happened to it mean. attribute whatsoever should be accurately defined. while, we call the two appearances identically the Hence a book of science must be a storehouse of defi
Next to this is the similarity of different speci- nitions as well as of propositions, although these last mens of the same substance or kind.
alone constitute information or truth. It is common The one science wholly founded on propositions of for parties in disputes to make each other define their similarity is mathematics.
terms—that is, to describe in some unmistakeable way The procedure of discovering and verifying these the attributes intended to be expressed by the general different classes of affirmations is different for each ; or abstract words made use of. But it requires a high and it belongs to Logic to prescribe methods for them degree of advancement in any science to furnish perall. It requires one style of investigation and of proof fect definitions of all the properties that it is concerned to establish propositions of causation or of fixed suc- with. The generalisation and the verification of a cession, and another set of operations to determine the definition is as much a process of discovery, and stands propositions of fixed co-existence; while the proposi- as much in need of human capacity and labour, as the tions of likeness are found in a way differing from generalisation and verification of a law. Hence it is either. Each of these methods will be alluded to when only in subjects which have attained a high scientific we come to speak of Induction.
development that accurate definitions are found. In
the abstruse sciences of mind and society, good definiDefinitiong.
tions are not in all cases attained, any more than good By far the most important distinction in the whole propositions. Thus the perfect definitions of will,' science of Logic, or in what constitutes the essence of virtue, beauty,” “poetry,'' genius, civilisation, can human knowledge, is the distinction between proposi- hardly be said to be as yet completely attained. tions and definitions; or between affirmations and con- As the things which go together by the ordination of ceptions, verbs and nouns. A definition we have al nature, or the conjunctions which, when expressed in ready shown to be the accurate expression and descrip- language, form propositions, are more frequently made tion of some abstract quality of which we have formed up of separate attributes than of complete objects, a conception, after a comparison of the different objects the importance of definitions as preparatory to proagreeing in the possession of such a quality. We stated positions must be evident. Thus when we say, 'electhat the final step in the process of abstraction was trical excitement is always polar, or consists of two the making of some accurate description of the pro- opposite excitements,' we state a proposition asserting perty abstracted, whether by words, by diagrams, by the conjunction of two very abstract attributes; and models, or by some specimen that contains the quality the proposition could not be discovered, nor proved, far as little mixed with others as possible. In short, the less affirmed and acted on, until a general idea was great end of a definition is to fix by some intellectual formed of electrical excitement, and likewise of polarity, machinery the character of an abstract conception, by the process of generalising and defining “The notion, or idea. But we have just found that a proposi- magnet has opposite poles,' is an instance of the same: tion couples together two ideas, and caunot possibly con- magnetism does not reside invariably in one concrete tain less. A definition communicates a notion or idea substance; it is a highly abstract property, sometimes to the mind, it gives us one conception more than we found in one substance, and sometimes in another. had previously, or communicates a perfect representation where perhaps we had only a vague idea before; but RATIOCINATION, OR ARGUMENTATIVE INFERENCE. it gives nothing that can be called knowledge, nothing Having ascertained the import of affirmations or proto be affirmed, or denied, or acted on; in respect of positions, we come next to consider the nature of proof, these matters, it is only one of the things that may enter or of the process that is gone through when an affirmainto a proposition. Two abstract ideas duly connected tion is said to be proved. In most cases of proof, may make a proposition; one idea never can. For the one or more affirmations are put forward which are purposes of discovery and of the investigation of nature, already believed or admitted to be true; and some new both definitions and propositions have to be sought; affirmation is derived from these, or said to be estabbut both must not be sought as if they were the same lished as following or flowing from them. 'John has thing. A definition and a proposition usually agree come to town: I saw him an hour ago;' is an assertion in this that they are both the results of generalising made and proved by the help of another assertion. from a number of instances; but the generalisation of You will get better by taking rest: I myself got an idea, and the generalisation of a law or a conjunc- round by that means;' is another example. It is a tion of ideas, should never be confounded. The im- part of Logic to ascertain the nature of the connection perfect recognition of this vital distinction is a source between one proposition and another, that will justify of much error and perplexity, both in matters of science the belief of the one on the faith of the other. and in questions of truth and falsehood apart from It has been shown by logicians, that when one asscience. In seeking a definition of an abstract pro- sertion is proved by the help of others, there are always perty, we ought to muster the individual objects in which at least two previous assertions necessary to make the it occurs; compare them together in order to obtain a proof. These two assertions have been technically clear picture of their common property; and finally, called premises, and the one that they prove is called invent some description, designation, or representation the conclusion. In ordinary cases, one of the premises which will so express and fix it, that other people may is a general proposition of any of the five kinds be able to conceive the property with the same rigid namely, Existence, Co-Existence, Succession, Causation, accuracy as the person who went through the labour or Resemblance; and the other premise is a proposition of making the comparison.
of resemblance. For example, the planets are round; All definitions must refer to something which does Neptune is a planet, therefore Neptune is round.' not itself require to be defined, or which is plainly and Here the first assertion is a general proposition of coclearly known to all men, and requires only to be existence, or an affirmation that certain bodies that named that it may be truly and justly conceived. circle round the sun have the attribute of roundness; Thus when the abstract property of roundness, or the or that the attribute of describing circles round the circular form, is defined in geometry, reference is made sun coincides with the attribute of roundness of form. to a central point and a straight line running out from, The second assertion is, that Neptune is one of the and revolving round it in the same plane. Now the planets, or is a body circling about the sun; or that he idea of a point, a straight line, and a plane, although resembles the bodies called planets, or that his peculi. they themselves are formally attempted to be defined arity of movement is like their peculiarity. The conin geometry, are examples of things so clearly per- clusion or inference is, that Neptune is a round body,
It is obvious that if we have obtained proof, or acquired | life of man suffices for obtaining a very extensive mascertainty in respect to the two assertions or premises tery of the vast and varied appearances of the world. in this case, there can be no doubt about the third; We have asserted that nature is uniform in her coinfor when it is shown that Neptune is entitled to be cidences of the properties of kinds, and in her succescalled a planet, that body is included in the sweep of sions of cause and effect. But, it may be asked, what the general proposition that all planets are round. proof have we to offer in support of this assertion, There are, therefore, always two things necessary in a which is of such magnitude and importance as to be step of argumentative proof: in the first place, a gene- the foundation of our proof of all other assertions, and ral proposition has to be established; and in the second the means of enabling us to convert a single case of place, an identification has to be made out between observation into an infinite belief? the subject of the general proposition and the subject There is no other proof to be offered for the uniforof the affirmation that is to be proved. This last point mity of nature than the unbroken experience of the huis merely the practical application of a general affirma- man race. Every age has found it so; and in the more tion to a special instance. The other step—the estab- recent times of human history, it has been tested in lishment of a general proposition-is the business of a every possible variety of ways, and no valid exception has scientific inquiry, and has to be done once for all by ever been recorded. There was a time when men might the proper machinery.
entertain doubts on the matter, or when the confirmaThe case we have now given of a step of deductive tion was but limited, and the apparent exceptions irreinference is an example of what is called a syllogism; concileable with the doctrine. But this time has now and it used to be reckoned the chief business of Logic gone by, and the principle has come to be established to lay down rules for the correct performance of this upon a basis that seems impossible to be shaken; and deductive inference, or for the shaping of valid syllo- all the future generations of men will rest upon it with gisms, the two assertions or premises being supposed unswerving confidence. Some have derived the proof of to be prored, or to have been previously ascertained to the principle from an instinct in human nature, which be true.* But it is now considered that the most se- leads us to expect this uniformity; but this is to rest rious and difficult part of the process of arriving at true upon a most perilous assumption-namely, that the conclusions, is the establishment of the general propo- native instincts of men can correctly anticipate the laws sitions which include them. By what process do we of the outer world-an assumption indeed that is far from come to be sure that all the planets are round-that true. The very same instinct which leads us to expect all men are mortal—that all matter gravitates—that uniformity in nature, also prompts us to believe that all chemical combinations take place in fixed propor-all other men are like ourselves; that our experience is tions? We must not merely provide for the correct the experience of the whole world; and that what is at application of propositions which have once been proved, variance with it must be false. It is the instinct that we must also provide for the proof of these fundamental urges the inhabitants of a tropical climate to denounce propositions themselves.
as liars and impostors the people who assert that water
can become solid like glass. Such an instinct is ut. INDUCTION.
terly untrustworthy, until corrected by the observation Induction is the term applied to the process of form of the actual world; but it is extremely valuable as an ing and establishing general propositions, principles, impulse advancing in the same general direction with laws, truths, or affirmations-that is, propositions which the results of our experience. are applicable not to one case only, but to all cases that The laws of causation, or the successions of events have a certain definable peculiarity; as when we say, established by nature, and invariably adhered to, make
gold is heavy,' in which case we affirm that all sub- the first and foremost subject of inductive investigastances having a certain colour and lustre are also of tion. In this case the great problem given for mangreat specific gravity.
kind to solve is to find the effects of all causes, and The first question that occurs to us respecting these the causes of all effects. general affirmations is—how and when are we entitled The general maxim of the uniformity of nature does to make such very broad assertions? We have no not always apply to the outward appearances of things. means of ascertaining the laws and coincidences estab. A south wind brings rain one day and drought another; lished in nature, except the observation of what the and in many other cases the law of strict succession world presents to us. ' If we see that the qualities of fails to hold good. The reason of this is discovered by yellowness and a peculiar lustre are combined with a very little examination : the superficial phenomena heaviness, we are entitled to assert the fact in as many of the world, the things that prominently arrest our instances as we have verified by examination. In like attention, are not single trains of causation, but mixmanner, if we see that water quenches fire, we may tures of many different trains; and the law of uniforassert that it is so in the cases noticed. But there mity does not necessarily hold good, except in the remains the grand difficulty --- namely, why are we simple and indivisible sequences of phenomena and entitled to say that these coincidences and successions events. No doubt if a certain number of causes acting take place not only in the cases where they have been together produce a certain amount of effects, the very observed, but also in the cases where they have not same combination will always produce like effects; but been observed, and in all cases whatever ? For this is it is not easy to make sure that two given combinations implied in every general proposition.
are really the same. In order to do so, we must first This question is answered by the fact, that nature is become acquainted with the simple causes one by one. uniform. There is a certain class of coincidences or Induction, therefore, in such a state of things, is essenco-existences which we have already alluded to as tight tially a process of analysis, or the separation of the co-existences, which are everlasting and unvaried, and complex threads of causation, with the view to deterneed only one observation to tell how they will be in mine the simple threads; and when we have once posevery variety of times and places; and there is a certain sessed ourselves of all these, we will be prepared to calclass of successions called Successions of Cause and culate the effects of any combinations of them. Nature Effect, that are of the like unchanging kind, being the rarely presents us with a cause and its effect standing same yesterday, to-day, and for ever. Hence, in these alone. The usual case is to have a multitude of effects cases, one observation is as good as a million; we are flowing from a multitude of causes. It requires, thereentitled to express or affirm infinitely more than we fore, the whole analytic force of the mind to be devoted actually find. It is from nature's repeating herself in to their reduction to single couples of cause and effect. endless ways that human labour is shortened to such This frequently involves a very difficult operation of an extraordinary degree, that a few years of the short the abstractive faculty.
The great object of inductive inquiry being to ascer* For a brief account of the Scholastic or Syllogistic Logic, tain among a multitude of connected things, which of seco Chambers's Journal,' No. 219, New Series.
them stand to each other in the relation of cause and
effect, we have now to consider the methods of observa-, bodies of their heat, nor exhibit it by itself and apart tion and experiment suited to this determination. By from all other things; and hence the methods above
experiment' is meant the process of altering the alluded to would entirely fail in determining what arrangements presented by nature, and shaping new things are connected with it as cause and effect. To arrangements of our own to assist us in ascertaining meet this difficulty, we have recourse to a method the simple sequences of cause and effect. Thus if na- named by Mr Mill the Method of Concomitant Variature presented to our observation a confused and com- tions--that is, in such a case as heat, we observe what plicated train, and if we contrive to remove a great effects increase as it increases, and diminish as it dimany of the circumstances, so as to reduce the train to minishes. The method is expressed in general terms a more simple sequence, we are said to proceed by as follows :- Whatever phenomenon varies in any man. experiment. If we find or observe a certain locality is ner whenever another phenomenon varies in some parti. exceedingly favourable to health; and if, in our wish to cular manner, is either a cause or an effect of that pheascertain which of all the peculiarities of the place is nomenon, or is connected with it through some fact the cause of the wholesomeness, we endeavour to put of causation. We very frequently proceed upon this ourselves into situations where each circumstance is method of observing the effects of the increased or excluded in turn, we are said to proceed experimen- diminished quantity of things, in order to see what tally. Mr Mill has laid down the different ways of effects they have a tendency to produce, judging rightly arriving at cause and effect by this experimental pro- that if one event be the cause of another, the two will cedure, under the title of the Four Experimental Me- rise and fall together. thods;' which he names the Methods of Agreement, of There are two kinds of complications that are beyond Difference, of Residues, and of Concomitant Variations. the reach of any of these four methods, and require a
• The simplest and most obvious modes of singling distinct treatment. The one is termed the case of the out from the circumstances which precede or follow a Plurality of Causes, the other the Intermixture of phenomenon those with which it is really connected as Effects. By a plurality of causes is meant, that it somean invariable law, are two in number: one is, by com- times happens that an effect may arise equally from paring together different instances in which the pheno- several causes, creating, as it were, an ambiguity of menon occurs; the other is, by comparing instances in causation. Thus a motion may arise from any one of which the phenomenon does occur with instances in a great number of forces; happiness or misery is proother respects similar, in which it does not. These two duced by innumerable agencies. In such cases, the methods may respectively be denominated the Method methods above stated are somewhat nonplussed, inasof Agreement, and the Method of Difference.
much as it may be possible to exclude one cause and In illustrating these methods, it will be necessary to yet keep in another. A still greater difficulty is prebear in mind the twofold character of inquiries into sented by the Intermixture of Effects—that is, when an the laws of phenomena; which may be either inquiries effect is not single, but complex. Thus the course of a into the cause of a given effect, or into the effects and projectile is not a single, ut a mixed effect, or two properties of a given cause.
different effects combined into one different from either. For example, let the antecedent be the contact of an The discovery of the cause or causes, under such cir. alkaline substance and an oil. This combination being cumstances, cannot be effected by the Experimental tried under several varieties of circumstance resembling Methods. But this leads us to the consideration of a each other in nothing else, the results agree in the pro- method different from any of these, which has a vast duction of a greasy and detersive or saponaceous sub- range of efficacy in scientific research, and becomes more stance. It is therefore concluded that the combination and more powerful as the sciences advance, or as disof an oil and an alkali causes the production of soap.' covery is extended. It is called the Deductive Method,
Mr Mill states the method of Agreement in a formal The Experimental Methods suppose that we take canon as follows:- If two or more instances of the pheno- up a subject that is as yet fresh and unexplored, or menon under investigation have only one circumstance in where no great general principles have been attained. common, the circumstance in which alone all the instances They are the methods adapted to the commencement of agree is the cause (or effect) of the given phenomenon. inquiry. But when one or two comprehensive laws
By the method of difference, is meant the process of have been arrived at, a great deal is to be discovered comparing two sets of circumstances--one containing the by following out the application of these laws wherever effect, and the other not; and where between the two they are found to operate. Thus when the law of the we can see no difference except in one other particular. perseverance of moving bodies was once discovered, it • When a man is shot through the heart, it is by this was made use of to explain many motions that would method we know that it was the gunshot that killed otherwise have remained inexplicable: such as the him; for he was in the fulness of life immediately rotation of the earth, and the tendency of the planets to before, all circumstances being the same, except the maintain their distance from the sun. In like manner, wound. This method is expressed as follows :- If an the discovery of the general law of reaction enabled instance in which the phenomenon under investigation Newton to determine the cause, and even for the occurs, and an instance in which it does not occur, have first time to ascertain the existence, of the fluctuation every circumstance except one in common, that one oc- of the sun in the centre of the planetary system. By curring only in the former, the circumstance in which the Deductive Method alone are we able to trace the alone the two instances differ is the effect, or cause, or a operation of that class of causes which, by intermixture, necessary part of the cause, of the phenomenon.
are wholly neutralised, and produce no apparent conseThe method of residues will be seen to be a carrying quences whatever-as in what are called the laws of out of the same attempt to break up complicated trains, equilibrium or counterpoise. and to fasten down the invariability of sequence upon There are three different steps in the complete work. the true particulars where cause and effect operate. It ing out of the Deductive Method. The first is Inducis stated thus:-Subduct from any phenomenon such tion, or the determination of the general law by the part as is known by previous induction to be the effect of Experimental Methods. The second is the carrying out certain antecedents, and the residue of the phenomenon is of the law to the explanation of all cases where it the effect of the remaining antecedents.
seems to apply, and especially the tracing out of the ' There remains a class of laws which it is impracti-action that would result from two or more principles cable to ascertain by any of the three methods which acting in combination. Thus the Deductive Method I have attempted to characterise-namely, the laws applied to trace out the cause of the curved motion of of those permanent causes, or indestructible natural a projectile, would consist in combining together the agents, which it is impossible either to exclude or to law of perseverance with the law of accelerated motion isolate, which we can neither hinder from being present, under a constantly-acting force, and in determining nor contrive that they shall be present alone. Heat is what would be the path that a body would describe an example of this kind of agents; we can neither divest | under the two actions. The third step, which is Veris