ly attested, is genuine and pure; it is the voice of Nature, and no fiction of human imagination.

73. The first rule of philosophizing laid down by the great Newton, is this:-"No more causes, nor any other causes of natural effects, ought to be admitted, but such as are both true, and are sufficient for explaining their appearances." This is the golden rule; it is the true and proper test, whereby what is sound and solid in philosophy may be distinguished from what is hollow and vain.

Corol. If a philosopher, therefore, pretend to show us the cause of any natural effect, whether relating to matter or mind, let us first consider whether there be sufficient evidence that the cause he assigns does really exist. If there be not, reject it with disdain, as a fiction which ought to have no place in genuine philosophy. If the cause assigned really exist, consider, in the next place, whether the effect it is brought to explain necessarily follows from it. Unless it have these two conditions, it is good for nothing.

CHAPTER IV.

OF ANALOGY.

74. It is natural to men to judge of things less known, by some similitude which they observe, or which they think they observe, between them and things more familiar or better known. This method of judging is called Analogy; and in many cases we have no better way of judging. And where the things compared have really a great similitude in their nature, when there is reason to think that they are subject to the same laws, there may be considerable degrees of probability in conclusions drawn from analogy.

Illus. Thus we may observe a very great similitude between this Earth which we inhabit, and the other planets, Herschel, Saturn, Jupiter, Mars, Venus, and Mercury. They all revolve round the Sun, as the Earth does, although at different distances, and in different periods of time. They all borrow their light from the Sun, as the Earth does. They revolve round their axes like the earth round her axis, and, by that means, must have a regular succession of day and night. Some of them have moons, which serve to give them light in the absence of the Sun, as our Moon does to us. They are all, in their motions, subject to the same law of gravitation as the Earth is. From all this similitude, it is not unreasonable to think, that those planets may, like our Earth, be the habitation of various orders of living creatures; nay, of sentient natures. There is some probability in this conclusion from analogy.

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75. In medicine, physicians must, for the most part, be directed in their prescriptions by analogy.

Illus. The constitution of one human body is so like to that of another, that it is reasonable to think, that what is the cause of health or sickness to one, may have the same effect upon another. And this is generally found true, though not without some excep

tions.

76. In politics we reason, for the most part, from analogy. The constitution of human nature is similar in different societies, or commonwealths; hence we conclude, that the causes of peace and war, of tranquillity and sedition, of riches and poverty, of improvement and degeneracy, are much

the same in all.

Corol. Analogical reasoning, therefore, is not, in all cases, to be rejected. It may afford a greater or a less degree of probability, according as the things compared are more or less similar in their nature. But it ought to be observed, that, as this kind of reasoning can afford only probable evidence, at best, so, unless great caution be used, we are apt to be led into error by it. For we are naturally disposed to conceive a greater similitude between things than there really is.

77. To give an instance of this. Anatomists, in ancient times, seldom dissected human bodies; but very often the bodies of those quadrupeds whose internal structure was thought to approach nearest to that of the human body. Modern anatomists, by the actual dissection of human bodies, have discovered many mistakes into which the ancients were led, by their conceiving a greater similitude between the structure of men and of some beast, than there is in reality.

Corol. By this, and many other instances that might be given, it appears that conclusions built on analogy stand on a slippery foundation; and that we ought never to rest upon evidence of this kind, when we can have more direct proof.

78. We form an early acquaintance, by means of our senses, with material things, and are bred up in a constant familiarity with them. Hence we are apt to measure all things by them; and to ascribe to things most remote from matter, the qualities that belong to material things.

Corol. It is for this reason that mankind have, in all ages, been so prone to conceive the mind itself to be some subtile kind of matter; that they have been disposed to ascribe human figure and human organs not only to angels, but even to the Deity!

79. We are conscious of the operations of our own minds, when they are exerted; we are even capable of attending to them, so as to form a distinct notion of them, but this is so

difficult a work to men, whose attention is constantly solicited by external objects, that we give them names from things that are familiar, and which are conceived to have some similitude to those operations; and the notions we form of them are no less analogical than the names we give them.

80. Almost all the words, by which we express the operations of the mind, are borrowed from material objects.

Illus. To understand, to conceive, to imagine, to comprehend, to deliberate, to infer, and many other words, are of this kind; so that the very language of mankind, with regard to the operations of the mind, is analogical.

81. Because bodies are affected only by contact and pressure, we are apt to conceive that what is an immediate object of thought, and affects the mind, must be in contact with it, and make some impression on it.

82. When we imagine any thing, the very word leads us to think that there must be some image in the mind of the thing conceived.

Corol. It is evident that these notions are drawn from some similitude conceived between body and mind, and between the properties of body and the operations of mind.

83. When a man is urged by contrary motives, those on one hand inciting him to do some action, those on the other to forbear it, he deliberates about it, and at last resolves to do it, or not to do it. The contrary motives are here compared to weights in the opposite scales of a balance; and there is not, perhaps, any instance that can be named of a more striking analogy between body and mind.

Corol. Hence the phrases weighing motives, deliberating upon actions, and the like, are common to all languages.

84. From this analogy, some philosophers draw very important conclusions. They say, that as the balance cannot incline to one side more than the other, when the opposite weights are equal, so a man cannot possibly determine himself, if the motives on both hands are equal; and as the balance must necessarily turn to that side which has most weight, so the will of the man must necessarily be determined to that hand where the motive is strongest.

Obs. And on this foundation, some of the schoolmen maintained, that if a hungry ass be placed between two bundles of hay, equally inviting, the beast must stand still and starve to death, being unable to turn to either, because the unfortunate animal has equal motives to both the bundles.

85. This is an instance of that analogical reasoning which

Dr. Reid conceives ought never to be trusted; for the analogy between a balance and a man deliberating, though one of the strongest that can be found between matter and mind, is too weak to support any argument. A piece of dead, inactive matter, and an active and intelligent being, are things very unlike; and because the one would remain at rest in a certain case, it does not follow that the other would be inactive in a case somewhat similar.

Illus. The argument is no better than this, that, because a dead animal moves only as it is pushed, and, if pushed with equal force in contrary directions, must remain at rest, therefore the same thing must happen to a living animal; for surely the similitude between a dead animal and a living, is as great as between a balance and a man.

Corol. The conclusion which results from all that has been said on analogy, is, that, in our inquiries concerning the mind and its operations, we ought never to trust to reasonings drawn from some supposed similitude of body to mind; and that we ought to be very much upon our guard, that we be not imposed upon by those analogical terms and phrases by which the operations of the mind are expressed in all languages.

CHAPTER V.

OF THE PROPER MEANS OF KNOWING THE OPERATIONS OF OUR OWN MINDS.

86. SINCE We ought to pay no regard to hypotheses, and to be very suspicious of analogical reasoning, it may be asked, from what sources must the knowledge of the mind, and its faculties, be drawn? I answer, from the three following. The first is attention to the structure of language; because the language of mankind is expressive of their thoughts, and of the various operations of their minds.

Illus. 1. Those operations which are common to mankind, have various forms of speech corresponding to them in all languages. These various forms of speech are the signs of the various operations of the understanding, will, and passions; and by those signs these operations are expressed. A due attention, therefore, to the signs, may, in many cases, give considerable light to the things signified by them.

2. But languages, from their imperfections, can never be adequate to all the varieties of human thought. There may, therefore, be things really distinct in their nature, and capable of being distinguished by the human mind, which are not distinguished in common

language. There may also be peculiarities in a particular language, of the causes of which we are ignorant, and from which, therefore, we can draw no conclusion. But whatever we find common to all languages, must have a common cause; must be owing to some common notion or sentiment of the human mind.

87. The second source of information on this subject, is a due attention to the course of human actions and conduct. The actions of men are effects; their sentiments, their passions, and their affections, are the causes of those effects; and we may, in many cases, form a judgment of the cause, by observing the effect.

Illus. 1. Thus, the behavior of parents towards their children gives sufficient evidence, even to those who never had children, that the parental affection is common to mankind. The general conduct of men, too, shows us what are the natural objects of their esteem, their admiration, their love, their approbation, their resentment, and of all their original dispositions. From the conduct of men in all ages, it is likewise obvious, that man is, by his nature, a social animal; that he delights to associate with his species; to converse, and to exchange good offices with them.

2. Not only the actions, but even the opinions of mankind, may sometimes give light into the frame of the human mind. The opinions of men may be considered as the effects of their intellectual powers, as their actions are the effects of their active principles. Even the prejudices and errors of mankind, when they are general, must have some cause no less general; the discovery of which will throw some light upon the frame of the human understanding.

88. The third, and main source of information, respecting the mind and its faculties, is accurate and attentive reflection upon the operations of our own mind. The power of the understanding to take notice of its own operations, to attend to them, and examine them on all sides, is the power of reflection; and all the notions we have of mind, and of its operations, have been called ideas of reflection.

Illus. 1. The term reflection implies nothing more than the deliberate and mature exercise of consciousness. But to acquire a habit of reflection upon the powers of our own minds, or of the deliberate exercise of consciousness, is a work of time and labor, even to those who begin early, and whose natural talents are tolerably fitted for it. This is the last of the powers of the mind that unfolds itself; and though many persons seem incapable of acquiring it in any considerable degree, it may be greatly improved by exercise. It is by the proper employment of this power that men become fitted to discover the laws by which their own thoughts are regulated, and to make advances in the science of intellectual philosophy.

2. When two persons are speaking to us at once, we can attend to either of them at pleasure, without being much disturbed by the