the logical necessity of the effect does not include the fact that power causes it to be, but arises because of the fact that power causes it to be; for, there being an adequate cause, the effect exists, and this cannot be otherwise.

Ratio cognoscendi and ratio essendi.

This difference between causal and logical necessity is the ground of the distinction between the ratio cognoscendi, or order of perception, and the ratio essendi, or order of existence. The order of perception is the same as that of logical necessity, in which the consequent is said to follow the antecedent, this meaning that its existence is connected with, and inferable from, that of the antecedent; but the order of existence is that of causal necessity, in which an effect literally follows its cause. The one order sometimes coincides with the other, but more frequently it does not. We cannot too firmly fix it in our minds that logical necessity, not causal, is the necessity referred to in every act of reasoning; and that when we say that a consequent exists because an antecedent exists, we do not mean to say that it is caused by the antecedent, but only that it necessarily exists as related to the antecedent. Inference depends upon conditions, not upon causes, upon causes only so far as they are conditions.

The relation of logical

necessity to

We have now discussed logical necessity as the external basis of inference. For in reasoning we inference ex- perceive a fact not immediately, but because of its actly defined. necessary co-existence with some known fact. The question, however, may now be asked, whether we do not, in the first place, simply perceive the fact as connected with the other fact, and then, as confirmation of this cognition, perceive the necessity of the co-existence, that the fact could not be otherwise. Such, we believe, is the case. That is, the perception of the concomitant fact does not depend on the perception of its necessity, but rather the reverse is true. For the necessity originates from the nature and relations of the fact, and therefore presupposes the fact. But a belief thus formed, if in any way questioned, is instantly confirmed by a perception of the necessity of the fact as related to the given fact; and such inferential belief is formed only in cases where this necessity exists. Evidently the mind has a wonderful power of suggestion, whereby, independently of any consideration of necessity, it sees things unseen as co-existent with, and related to, things But the unseen, while thus perceived, is always necessarily co-existent and related, and may be viewed also in this light. Logical relations are always necessary relations. We infer only such things as have some necessity of existence, either absolute or relative. If one should classify the necessary rela

seen.

tions of fact, he would classify also the various modes of inference. The doctrine of necessity, and of things as necessarily related, cannot be separated from the doctrine of reasoning.

An old defi

CHAPTER XXI.

LOGICAL POSSIBILITY.

1. LOGICAL possibility- that is, possibility in general, nition dis- considered as the basis of a certain mode of reasoningcussed and has been thus defined in scholastic language: "Possibilitas amended. est consensio inter se, seu non-repugnantia, partium vel attributorum quibus res, seu ens, constituatur." This might be rendered: "Possibility is the mutual harmony, or non-repugnance, of the parts, or attributes, which constitute any thing, or entity."

To this statement it may be properly objected that the parts of a possible object must not only harmonize with each other, but that they, and the object as a whole, must also harmonize with other things, that is, with the circumstances in which the object is supposed to exist.

Let the problem be to construct a square with four straight lines of different lengths. We say, this is impossible, because a plane figure with four sides of different lengths cannot contain right angles. The parts of such a thing are conflictive with one another. There is no contradiction, however, in the idea of a square with four straight sides of equal length. The parts of such a figure are mutually compatible; and, in general, it is clear that the parts of a thing possible must be compatible with one another. But it is also evident that the construction of a square of a given area is possible only on a plane surface of sufficient dimensions; for example, a blackboard. It would be impossible to make such a figure on a spherical surface, or on a plane surface less than itself in area. This shows that the parts, or elements, of the object must harmonize, not only with each other, but also with the circumstances in which the object is perceived, or supposed, to exist. We may, indeed, justify the scholastic definition by so enlarging our conception of the thing possible as to take in the given circumstances. We may make these, as it were, parts of the object. Thus "a square with a side of four inches on a board six inches by six" may be regarded as one possible object; and "a square with a side of eight inches on a board six by six" as one impossible object. But this comprehensive mode of conception is not one generally employed. Philosophers should adapt their language, when this is possible, to common modes of thought; and in the present case it would be better to say that possibility is the harmony of the parts of an object with each other and with given surroundings.

But let us note, further, that, ordinarily, the internal possibility of a thing is taken for granted; so that our inquiry, for the most part, concerns only external possibility. An animal is a thing internally possible, because its parts may co-exist; and it is externally possible where there are food and air and other necessaries. When we ask whether animal life is possible in some distant region of the universe or amid the surroundings of some past geologic age, our question evidently limits itself to the thought of the compatibility of animal life with certain external circumstances pertaining to food, air, climate, and so forth. Indeed, our common mode of thinking being directed almost exclusively to external consistencies, ordinary logical possibility might be defined simply as the compatibility of a thing with given surroundings; in which definition, however, the presupposition is involved, that the parts, or attributes, of the thing are harmonious with each other. A very wide definition of possibility is that it is the compatibility of one thing with another, or with others, with which it may be perceived, or supposed, to co-exist. This statement covers both external and internal possibility; for it implies both that the parts mutually harmonize, and that the object, as a whole, is compatible with given circumstances.

The words "harmony" and "compatibility" ordinarily Logical possibility is an mean that two or more persons have such dispositions that existential they live together in peace and without hatred; or that compatidifferent notes of music are such that they do not make a bility. disagreeable but a pleasant sound; or that two trades or occupations are such that both may be profitably pursued at the same time by the same person. In such cases the compatibility of two or more things allows the existence of another thing, while their incompatibility would prevent the existence of that other thing. According to this use of terms, incompatible things may exist together, but cannot be attended with peace or pleasure or profit. When, however, we speak of logical compatibility or incompatibility, we mean simply that two things are such that they may exist together, the one with the other, or that they are such that they cannot exist together. Logical possibility, therefore, might be defined as the existential harmony of one thing with others. Yet even this should be accepted as presenting rather an analogy than an analysis; for the relation of existential compatibility has something in it ultimate and sui generis. The thought of it is very simple, like that of existence or of nonexistence; and it is to be contrasted with the relation of logical confliction, or repugnance, very much in the same way that existence is to be contrasted with non-existence.

The radical

The most important question touching logical possibility law of infer- concerns the mode in which the mind determines respecting ence in pos- anything whether it be possible or not. This leads to the sibility. remark that the doctrine of possibility, like that of necessity, is intimately related to the doctrine of conditions, that is, to the doctrine of the necessary conditions of a thing. For here, to avoid confusion, we must distinguish two senses in which the term "condition" may be used in connection with the subject of possibility; because if one should ask, Is such a thing possible under such and such condi

tions? it is plain that he would not be speaking of the necessary conditions of the existence of a thing. It would be foolish to ask whether a thing is compatible with the necessary conditions of its existence. He would simply mean, Is the thing possible under such and such circumstances? In the present discussion let us employ the word circumstances" for those given or supposed facts with which something may be affirmed or denied to be possibly co-existent. And let us confine the term "condition" to the necessary conditions of the existence of a thing. We have already seen that these conditions may be divided into three classes, - the constitutive, the causal, and the concomitant.

Now it is self-evident that a thing can exist only where the necessary conditions of its existence can exist, in other words, the compatibility of a thing with given circumstances involves also the compatibility of its conditions with those circumstances. Therefore, when a thing is possible in its constitutive, causal, and concomitant conditions, it is possible in every respect; and the possibility of a thing may be determined by determining the possibility of its conditions. This radical principle is the most important in the philosophy of the possible.

Very little examination will satisfy any one that inferences in possibility take place according to the law just mentioned. After it is settled that the thing in itself — that is, in its constitutive conditions -is possible, we naturally proceed to discuss whether its causal and concomitant conditions, severally, be compatible with the case or not. After it had been decided that a telegraphic wire twenty-five hundred miles in length could be made and operated, the further questions arose: Can it be insulated against the pressure of great weights of water? Can it be let down to the bottom of the ocean without twisting and breaking it? Can machinery be devised for the construction of it, and vessels be procured for its conveyance? And can the confidence of capitalists be obtained, so that the necessary expenses may be met? The first Atlantic cable followed upon an affirmative answer to these questions. Evidently we infer the possibility of a thing from the possibility of its conditions.

The postu

To some this statement may present a difficulty. It may lates of pos- be said: If the possible involve possible conditions, will sibility. not these involve yet other possible conditions, and these still others; and so will not an infinite regression be needed to establish any possibility? We reply that it would be needed were there not conditions whose possibility is self-evident. But an immediate perception of possibility takes place in several ways.

In the first place, whatever actually exists in any given circumstances, exists under every one of its necessary conditions, and is possible in every respect. Hence in those frequent cases in which a condition actually exists, there is no need of inquiry as to the possibility of that condition.

In the second place, whatever has existed may, in similar circumstances, exist again; and this principle enables us to determine the possibility of a condition which, though not known to be fact, is known exactly to resemble fact. For the thought of possibility per

tains to forms conceived of as existing, and not to real things as such; and we may at once, and once for all, perceive a form to be possible. Finally, in other cases there is no regression, because the radical, or ontological, elements and conditions of things, such as spaces, times, powers, substances, actions, and changes, - in the various relations according to which these condition one another, are immediately recognized by the mind as possible. Thus many radical conceptions of things possible are formed. In the use of these conceptions, in which the possibility of the ontological character and conditions of a thing is asserted, other and less abstract possibilities are determined. We say it is possible for a bushel measure to contain a peck of potatoes. This is simply the concrete operation of the principle that what can contain the greater can contain the less. But this law of the possible in spacial measures, together with the possibility of its conditions, such as space, substance, quantity, and the mutual relations of these things according to the terms of the law, is immediately perceived by the mind. Such ultimate conceptions or judgments may be styled the first principles, or postulates, of possibility. Like our conceptions of fundamental necessities, they seem to be originally formed by the mind during its perception of facts.

-

The foregoing remarks show how the statement is to be taken that the possibility of a thing must be inferred from that of its conditions. Of course, when possibility is self-evident, it need not be perceived inferentially; in a large number of cases it may be immediately perceived, and therefore need not be proved.

The asser

the denial of

2. Such are the essential points in the doctrine of logical possibility. But an exact understanding of this doctrine calls for some supplementary statements. First, let us note that although the conception of possition of possibility involves the conception of existence, the assertion of bility does possibility does not, of itself, involve the assertion either of not involve existence or of non-existence. A thing is possible in that existence. it is possible to be, or as to its existence. Therefore, to determine the question of possibility, we have first to conceive of a thing as existing, and then to ask whether its existence is compatible with the given circumstances. But while we must conceive or imagine the thing in question to exist, we do not assert either that it is or that it is not. The assertion of possibility, in itself, only states that if a certain thing should exist it would harmonize with given circumstances; it does not say whether the thing exists or not.

Frequently, indeed, we ask whether a thing not now existing may be realized in the future, or may have been realized in the past; and then, combining the idea of non-existence with that of possibility, we mean by the possible the merely possible, the non-existent possible. This limitation of thought is implied, also, when we contrast the possible with the actual, when, for example, we speak of all things actual and of all things possible. In such cases there is an addition made to the simple idea of possibility of something which is non-essential to that idea; for we can also say that a thing is not only possible but actual, and that it is possible because it is actual. The transmission of thought through the depths of the ocean is possible because it is a