operation; but in regard to all of them reason is our ultimate guide in judging whether they are performed in a legitimate manner, and upon principles calculated to lead to the discovery of truth. These processes may be chiefly referred to the following heads :—

I. To make a careful collection of facts relating to the subject, and to abstain from deducing any conclusions till we have before us such a series as seems calculated to warrant them. The first operation of reason therefore is, to judge when we have a sufficient number of facts for this purpose.

II. To separate from the mass those facts which are connected with it incidentally, and to retain those only which we have reason to consider as uniform and essential. In some sciences this is accomplished by repeated and varied experiments; and in those departments which do not admit of this, it is done by cautious and extensive observation. Our object in both cases is to ascertain how many of the circumstances observed, and what particular combinations of them uniformly accompany each other, or are really connected with the effects which are produced. In this careful clearing of our statement from all incidental combinations consists that faithful observation of nature which forms the first step in every scientific investigation. It is opposed to two errors, both equally to be avoided, namely, leaving out of view, or not assigning an adequate value to, important and essential facts; and giving a place and an importance to those which are incidental and trivial. In every scientific investigation this is a process of the utmost importance; and there is another nearly connected with it, namely, to judge of the authenticity of the facts. This also is a mental process of the utmost delicacy. In conducting it, there are two extremes from which the exercise of sound judgment ought equally to guard us, namely, receiving facts upon imperfect evidence, and rejecting those which have a sufficient title to credit; in other words, credulity and scepticism. Both these extremes are equally unworthy of a mind which is guided by sound reason.

Classification of mental processes necessary for the investigation of truth? First head; collecting facts. Second head; selecting those which are essential. Two errors to be avoided? Two extremes in regard to the admission of facts?

III. To compare facts with each other, so as to trace their resemblances, or to ascertain those characters or properties in which a certain number of facts or substances agree. We thus arrange them into classes, genera, and species.

IV. To compare facts or events with each other, so as to trace their relations and sequences; especially that relation of uniform sequence on which is founded our notion of cause and effect. This delicate and most important process consists entirely in a patient observation of facts, and of their relation to each other. When, in a certain number of instances, we find two events following one another without any exception, we come to consider the sequence as uniform, and call the one cause, and the other effect; and when, in other instances, we are disappointed in finding such a succession, this confidence is shaken, unless we can discover a cause by which the sequence was interrupted. Reason, acting upon extensive observation, must here guide us; on the one hand to judge of the uniformity of the sequences, and, on the other, to account for apparent deviations.

V. To review an extensive collection of facts, so as to discover some general fact common to the whole. This is the process which we call generalizing, or the induction of a general principle. The result of it is the last and greatest object of human science, and that to which all the other steps are preliminary and subservient. An ordinary mind is satisfied with the observation of facts as they pass before it, and those obvious relations which obtrude themselves upon its notice; but the philosopher analyzes the phenomena, and thus discovers their more minute relations. His genius is distinguished above the industry of the mere observer of facts, when he thus traces principles of accordance among facts which, to the vulgar eye, appear remote and dissimilar. A remarkable example of this is familiar to every one. Between the fall of an apple from a tree and

Third head; comparison of facts with reference to their nature. Fourth head; comparison of facts with reference to their causes and relations. Fifth head generalizing The operation of an ordinary and of a philosophical mind compared.

the motions of the heavenly bodies a common mind would have been long ere it discovered any kind of relation; but on such a relation Newton founded those grand principles by which he brought to light the order and harmony of the universe. For it was this simple fact that first suggested to him the great principle of physical science, that matter attracts matter in the reciprocal ratio of their masses.

In a practical view, these processes may be referred to three heads, namely, collecting authentic facts,-tracing causation, and deducing general principles. Here various mental operations are brought into action, especially attention, memory, conception, and abstraction; but it is the province of reason to judge whether these are conducted in a legitimate manner, or, in other words, to distinguish truth from falsehood. It may, therefore, be important to keep in mind what those circumstances are in which consist truth and falsehood, in reference to any department of knowledge.

I. In collecting facts, it is required in the first place that they shall be authentic; secondly, that the statement shall include a full and fair view of all the circumstances which ought to be taken into our investigation of the case; and thirdly, that it shall not include any facts which are not connected with the subject, or whose connection is only incidental. When we have thus formed a collection of facts, authentic, full, and essential, the statement, in as far as relates to the facts, constitutes truth. When any of the facts are not authentic; when important facts are left out of the statement, or misrepresented; or when facts are taken into it which, though true, have no real relation to the subject; this constitutes fallacy or falsehood.

II. In considering two events as connected in the manner of cause and effect; when this relation is deduced from a full and extensive observation of the sequence being uniform, this is truth. When it is assumed upon inadequate grounds, that is, from the observation of a connection which is only incidental or limited,—this is either falsehood or hy

Example? More general classification of these processes? Three principles to be observed in collecting facts. Principles to be observed in determining the relation of cause and effect?

pothesis; for the relation may be assumed upon grounds which, though not actually false, are yet not sufficient to establish it as true-namely, on observation which is too limited in extent. This is conjecture or hypothesis; and it is in some cases a legitimate process, provided it be used only as a guide for further observation, and be not received as true until such observation shall have been sufficient to confirm it.

III. In deducing from a large collection of facts a general fact or general principle; when this induction is made from a full examination of all the individual cases to which the general fact is meant to apply, and actually does apply to them all, this is truth. When it is deduced from a small number of observations, and extended to others to which it does not apply, this is falsehood. As in the former case, however, a general principle may be produced hypothetically or by conjecture; that is, it may be assumed as general so far as we at present know. This process is often legitimate and useful as a guide in further inquiry, if it be employed for this purpose only, and the result be not received as truth until it be established by sufficient observation. A great and not unfrequent error is, that when such hypothetical principles are proposed in a confident manner, they are very often received as true; and the consequence is, that a degree of observation is required for exposing their fallacy, perhaps as extensive as, if properly employed, might have been sufficient to discover the truth. Those who are acquainted with the history of medical doctrines will be best able to judge of the accuracy of this observation, and to estimate the extensive influence which this error has had in retarding the progress of medical science.

The proper rules to be observed, in deducing a general principle, are therefore opposed, in the first place, to the error of hasty generalizing, or deducing such a principle from a limited number of facts. They are further opposed to another error, prevalent in the hypothetical systems of the old philosophy, by which phenomena were referred to principles altogether fictitious and imaginary, or, in other words,

Principles to be observed in deducing general laws. False deductions. Hypothesis; its legitimate use? Abuse of it? Common errors ?

which could not be shown to be facts. In opposition to both these errors the great rule of induction in modern science is, that the principle which is assumed as general shall be itself a fact, and that the fact shall be universal. Thus, what we call the law of gravitation is primarily nothing more than the fact that bodies fall to the earth; and that this is true of all bodies, without a single exception. Of the cause of this fact, or the hidden principle on which it depends, we know nothing, and all the investigations of Newton were carried on independently even of the attempt to discover it. "When Newton," says Mr. Stewart, "showed that the same law of gravity extends to the celestial spaces, and that the power by which the moon and planets are retained in their orbits is precisely similar in its effects to that which is manifested in the fall of a stone; he left the efficient cause of gravity as much in the dark as ever, and only generalized still further the conclusions of his predecessors."

False investigation may be briefly referred to three heads -fallacies in facts,-false inductions,-and false reasoning.

I. FALLACIES IN FACTS. A statement of facts is fallacious when any of the alleged facts are not true,—when it includes facts not relating to the subject, and when important facts are omitted. This last error is most frequently exemplified in those cases in which facts are collected on one side of a question, or in support of a particular doctrine. To the same class we may likewise add those instances in which statements are received as facts which are not facts, but opinions.

II. FALSE INDUCTION includes false causation and false generalization. False causation is, when two events are considered as cause and effect without sufficient reason, and which are, in fact, only incidentally combined; when events are considered as cause and effect which are only joint effects of a common cause; and when, of two events really connected as cause and effect, we mistake the order

Great rule of induction? Examples. False investigation; referred to how many and what heads? First head? Second head ?