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tected by later anatomists. It does not follow, because things resemble each other in a multitude of particulars, that this resemblance will be found in all others; and we are, therefore, always to consider ourselves in danger of pushing the supposition of similitude too far.
The proper use of analogical reasoning seems to be, in all scientific inquiries, merely to illustrate and confirm truths which are susceptible of proof from other sources of evidence, either by casting a direct additional light or by answering objections. A happy instance of this use of it is the work of Bishop Butler, entitled, "The Analogy of Religion, natural and revealed, to the Constitution and Course of nature."-It is not the object of the writer to prove the truth of religion, but to answer some objections which may be brought against its practical details and its principles by those who, while they object to the Bible, still maintain the existence of a God. And this he does by proving that the same objections exist to the providence of God in the natural world. There is an Analogy or resemblance in the two, viz., between the administration of God as made known in the Bible, and his administration of things as made known in the natural world; and if the objections which are brought forward will reject him from the authorship of what we term Religion, they will dethrone him also, for the same reason, from all authorship and direction in the ordinary economy of nature.
293. Of reasoning by induction.
We now come to another method of moral reasoning, viz., by induction. Inductive reasoning is the inferring of general truths from particular facts that have fallen under our observation. Our experience teaches us that nature is governed by uniform laws; and we have a firm expectation (whether it be an original principle of our constitution, or whatever may be the origin of it) that events will happen in future, as we have seen them happen in times past. With this state of mind we are prepared to deduce inferences by induction.
When a property has been found in a number of subjects of the same kind, and nothing of a contradictory
nature appears, we have the strongest expectation of finding the same property in all the individuals of the same class; in other words, we come to the conclusion that the property is a general one. Accordingly, we apply a magnet to several pieces of iron; we find in every instance a strong attraction taking place; and we conclude, although we have made the experiment with only a small number of the masses of iron actually in existence, that it is a property of iron to be thus affected by that substance, or that all iron is susceptible of magnetical attraction. This is a conclusion drawn by induction.
The belief which attends a well-conducted process of inductive reasoning bears a decided character; it is moral probability of the highest kind, or what is sometimes termed moral certainty; and is at least found to be sufficient for all practical purposes. We obtain all the general truths relating to the properties and laws of material objects in this way.
And we thus not only acquire a knowledge of material objects, but apply the same inductive process also in the investigation of laws which govern the operations of the mind. It is by experience, or observing what takes place in a number of individuals, that we are able to infer the general law of association, viz., when two or more ideas have existed in the mind in immediate succession, they are afterward found to be mutually suggested by each other. It is the same in ascertaining other general laws of the mind.
294. Of the caution necessary in inductive processes.
Reasoning in this method requires the exercise of caution no less than by analogy. It is especially liable to prove fallacious, whenever our investigations have been marked with impatience, and our judgments are formed on a very small number of facts.
When the number of examined instances is large, and the results are uniform, the conclusion amounts to moral certainty. But when the number of such instances is small, and the results are not altogether uniform, the judgments formed wil. possess a greater or less degree of probability, varying with circumstances.--And espe
cially is the mind left in a state of vacillation and uncertainty, when results have repeatedly occurred under such circumstances as to leave us at liberty to ascribe them to a diversity of causes. In such cases we find ourselves
reduced to the necessity of resorting to what writers on this subject have termed INSTANTIE CRUCIS.-The impor tant and decisive method in Inductive Reasoning of IN STANTIE CRUCIS was first laid down in the Novum Organum of Bacon, and has recently been happily illustrated in Playfair's View of the Progress of Mathematical and Physical Science in the following terms.
◊ 295. Of instances or experiments in inductive reasoning termed in stantiæ crucis.
"When the understanding is placed in equilibrio, as it were, between two or more causes, each of which accounts equally well for the appearances, as far as they are known, nothing remains to be done but to look out for a fact which can be explained by one of these causes and not by the other; if such a one can be found, the uncertainty is removed, and the true cause is determined. Such facts perform the office of a cross, erected at the separation of two roads, to direct the traveller which he is to take, and on this account Bacon gave them the name of instantiæ crucis.
"Suppose that the subject inquired into were the motion of the planets, and that the phenomena which first present themselves, or the motion of these bodies in longitude, could be explained equally on the Ptolemaic and the Copernican system, that is, either on the system which makes the Earth, or that which makes the Sun, the centre of the planetary motions, a cautious philosopher would hesitate about which of the two he should adopt; and, notwithstanding that one of them was recommended by its superior simplicity, he might not think himself authorized to give to it a decided preference above the other. If, however, he consider the motion of these bodies in latitude, that is to say, their digressions from the plain of the ecliptic, he will find a set of phenomena which cannot be reconciled with the supposition that the Earth is the centre of the planetary motions, but
which receive the most simple and satisfactory explana tion from supposing that the sun is at rest, and is the centre of those motions. The latter phenomena would therefore serve as instantiæ crucis, by which the superior credibility of the Copernican system was fully evinced "*
296. Of combined or accumulated arguments.
When a proposition in geometry is given to be demonstrated, it sometimes happens that two or more solutions may be offered leading to the same end. The theorem or the problem is one and the same, as also the conclusion; but there may be more than one train of reasoning, more than one series of intermediate steps, connecting the proposition which is to be investigated with the result. But as the conclusion in each of these different cases is certain, it does not strengthen it, although it may gratify curiosity to resort to a different and additional process.
It is not thus in moral reasoning. The great difference between the two kinds of reasoning, as before observed, is not so much in the mental process as in the subjects about which they are employed. Now as the subjects in moral reasoning are not of a purely abstract nature, and are, therefore, often attended with uncertainty, our belief, when we arrive at the conclusion, is not always of the highest kind. More frequently it is some inferior degree of probability. Hence, in any moral inquiry, the more numerous the series of arguments which terminates in a particular conclusion, the stronger will be our belief in the truth of that conclusion.
Thus we may suppose a question to arise, Whether the Romans occupied the island of Great Britain at some period previous to the Saxon conquest? In reference to this inquiry a number of independent arguments may be brought forward: (1.) The testimony of the Roman historians; (2.) The remains of buildings, roads, and encampments, which indicate a Roman origin; (3.) The coins, urns, &c., which have been discovered. Although these arguments are independent of each other, they all
* See Works of John Playfair, Esq., Edinburgh edition, vol. ii.,
bear upon the same conclusion; and, being combined together, they very essentially increase the strength of our belief.
PRACTICAL DIRECTIONS IN REASONING.
297. Rules relating to the practice of reasoning.
VARIOUS directions have been given by writers on Logic (which, it may be remarked here, is only another name for whatever concerns the nature, kinds, and applications of reasoning), the object of which is to secure the more prompt, accurate, and efficient use of the reasoning power. It is but natural to suppose that some of these dialectical rules are of greater, and others of less value. Such as appeared to be of the least questionable importance are brought together and explained in this chapter; nor will this occasion any surprise when it is recollected that it has been the object of this Work throughout, not only to ascertain what the mental operations are, but, by practical suggestions from time to time, to promote what is of a good, and prevent what is of a hurtful tendency in such operations.
The directions now referred to have of course a more intimate connexion with Moral than with Demonstrative reasoning; but this is a circumstance which enhances rather than diminishes their worth. The occasions which admit and require the application of moral reasoning, being inseparable from the most common occurrences and exigences of life, are much more numerous than those of demonstrative reasoning.
298. Of being influenced in reasoning by a love of the truth. (L.) The first direction in relation to reasoning which will be given, concerns the feelings with which it is proper to be animated. It is this. In all questions which admit of discussion, and on which we find ourselves at Vol. I.-I 1