and essential parts. It analyzes the structure of arguments, and shows how their truth may be discovered, or their fallacy detected. Lastly, it describes those methods of classification and arrangement, which will best enable us to retain and apply the knowledge, which we have acquired.

3. Though the understanding would be incapable of any high degree of improvement, without the aid of rules and principles, yet these are insufficient without practice and experience. The powers of the mind, like those of the body, must be strengthened by use. The art of reasoning skilfully can be acquired only by a long and careful exercise of the reasoning faculty, on different subjects and in various ways. The rules of logick afford assistance to this faculty, not less important than that, which our animal strength derives from the aid of mechanical powers and engines. They guide its operations, and supply it with suitable instruments for overcoming the difficulties, by which it would be impeded in its search after truth.

4. In the following compend, the subjects of logick are distributed into three parts. The

first contains a brief description of the leading powers and operations of the mind: The second, of the several kinds of terms and propositions. The third comprises an explanation of moral and demonstrative evidence; of the different modes of reasoning; of sophisms; and of method, or disposition.

CHAPTER FIRST.

PERCEPTION AND CONSCIOUSNESS.

5. Perception is the first state or affection of the human mind. By this we gain all our knowledge of the powers and qualities of the material objects about us. The instruments of perception are the five corporeal senses, seeing, feeling, hearing, tasting, and smelling. All the intercourse, which the mind has with the material world, is carried on by these organs. Of the manner, in which this intercourse proceeds, we have no knowledge. From experience we learn, that a sensible alteration takes place in the mind, whenever any outward object is so situated, as to affect either of the senses. The change, produced in the mind by the impression of the object on the organ of sense, is denominated sensation.

The word perception denotes the knowledge, that we gain by sensation, of some quality in the object; which knowledge may be retained by the mind after the object is removed, and it is then usually called an idea or notion. The external object, or quality perceived, is denominated the object of perception, or the archetype of the idea.

6. If either of the senses be wholly wanting, the mind must be forever destitute of all that class of ideas, which it is the office of that sense to furnish. If either be possessed but imperfectly, the ideas, received from it, are liable to be faint and indistinct. But the usual effects of dull organs may be in a great measure obviated, by an increased effort of attention, while the objects are present; as is manifest in the case of persons, who have had their hearing in some degree impaired.

It is from habitual inattention to our sensations, more than from dulness in the organs

"The sensations, which are excited in the mind by external "objects, and the perceptions of material qualities, which follow those "sensations, are to be distinguished from each other only by long "habits of patient reflection." Stewart, Elem. vol. i. ch. v

sect. 1st.

part 2d

of sense, that so few of the objects, which strike our senses, leave any durable traces in the mind; and that those notions, which do remain, are so often obscure and indistinct. As the perceptions of sense are the first elements of our knowledge, we should cultivate the habit of carefully noticing the things, which we see, feel, and the like; in order that the notions, which we form of them, may be clear and distinct.

7. Consciousness, or reflection, is that notice, which the mind takes of its own operations, and modes of existence.* By this we are made acquainted with the successive changes, which take place in the state of our minds. Consciousness is similar to perception, though the qualities of body, which are the objects of the latter, bear no resemblance to the thoughts and operations of the mind, which are the objects of the former. The mind, at least whilst we are awake, is constantly employed in some mode of thinking, or in some exertion of its powers; and all the operations, passions, and affections of the mind, are necessarily subject to its own observation. Thus, by

* See note A, at the end of the book.

consciousness, we learn what is expressed by the words compare, reason, doubt, assent, joy, in the same manner as, by perception, we gain a knowledge of sweet, green, soft, cold.

8. Both perception and consciousness, considered apart from any acts of attention, accompanying them, are involuntary states of mind. We are often active in bringing external objects within our view, and in varying their position, for the purpose of careful observation; so, by a voluntary effort, we excite operations, and cause changes in the mind; but the knowledge, that we gain in each case, of the subjects thus presented, is without any act of the will. We cannot avoid hearing many sounds, and seeing the objects, which are placed before our eyes. We are constrained to smell odours, taste our food, and feel bodies, when in contact with our own. It is the same with respect to the operations and states of the mind. We are unable to compare, reason, abstract; to feel pain, pleasure, disgust, or the like, without being conscious of those states.