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TREATISE OF HUMAN NATURE.
Book I. Of the Understanding, p. 5 to the end, p. 347.
Book III. Of Morals, p. 219—p. 415. DIALOGUES CONCERNING NATURAL RELIGION, p. 419—p. 548.
APPENDIX TO THE TREATISE, p. 551—p. 560.
ESSAYS, MORAL AND POLITIJAL, p. 3—p. 282.
POLITICAL DISCOURSES, p. 285—p. 579.
AN INQUIRY CONCERNING HUMAN UNDERSTANDING, p. 3–
AN INQUIRY CONCERNING THE PRINCIPLES OF MORALS, P. 237 —
THE NATURAL HISTORY OF RELIGION, p. 435—p. 513.
ADDITIONAL ESSAYS, p. 517—p. 577.
As the volume and the page of the volume are given in my references, it will be easy, by the help of this table, to learn where to look for any passage cited, in differently arranged editions,
THE OBJECT AND SCOPE OF PHILOSOPHY.
Kant has said that the business of philosophy is to answer three questions : What can I know? What ought I to do? and For what may I hope? But it is pretty plain that these three resolve themselves, in the long run, into the first. For rational expectation and moral action are alike based upon beliefs; and a belief is void of justification, unless its subject-matter lies within the boundaries of possible knowledge, and unless its evidence satisfies the conditions which experience imposes as the guarantee of credibility.
Fundamentally, then, philosophy is the answer to the question, What can I know ? and it is by applying itself to this problem, that philosophy is properly distinguished as a special department of scientific research. What is commonly called science, whether mathematical, physical, or biological, consists of the answers which mankind
have been able to give to the inquiry, What do I know? They furnish us with the results of the mental operations which constitute thinking ; while philosophy, in the stricter sense of the term, inquires into the foundation of the first principles which those operations assume or imply.
But though, by reason of the special purpose of philosophy, its distinctness from other branches of scientific investigation may be properly vindicated, it is easy to see that, from the nature of its subject-matter, it is intimately and, indeed, inseparably connected with one branch of science. For it is obviously impossible to answer the question, What can we know? unless, in the first place, there is a clear understanding as to what is meant by knowledge ; and, having settled this point, the next step is to inquire how we come by that which we allow to be knowledge; for, upon the reply, turns the answer to the further question, whether, from the nature of the case, there are limits to the knowable or not. While, finally, inasmuch as What can I know? not only refers to knowledge of the past or of the present, but to the confident expectation which we call knowledge of the future ; it is necessary to ask, further, what justification can be alleged for trusting to the guidance of our expectations in practical conduct.
It surely needs no argumentation to show, that the first problem cannot be approached without the examination of the contents of the mind; and the determination of how much of these contents may be called knowledge. Nor can the second problem be dealt with in any other fashion; for it is only by the observation of the growth of knowledge that we can rationally hope to discover how knowledge grows. But the solution of the third problem simply involves the discussion of the data obtained by the investigation of the foregoing two.
Thus, in order to answer three out of the four subordinate questions into which What can I know? breaks up, we must have recourse to that investigation of mental phenomena, the results of which are embodied in the science of psychology.
Psychology is a part of the science of life or biology, which differs from the other branches of that science, merely in so far as it deals with the psychical, instead of the physical, phenomena of life.
As there is an anatomy of the body, so there is an anatomy of the mind; the psychologist dissects mental phenomena into elementary states of consciousness, as the anatomist resolves limbs into tissues, and tissues into cells. The one traces the development of complex organs from simple rudiments; the other follows the building up of complex conceptions out of simpler constituents of thought. As the physiologist inquires into the way in which the so-called “functions” of the body are performed, so the psychologist studies the so-called “faculties” of the mind. Even a cursory attention to the ways and works of the lower animals suggests a comparative anatomy and physiology of the mind; and the doctrine of evolution presses for application as much in the one field as in the other.
But there is more than a parallel, there is a close and intimate connexion between psychology and physiology. No one doubts that, at any rate, some mental states are dependent for their existence on the performance of the functions of particular bodily organs. There is no seeing without eyes, and no hearing without ears. If the origin of the contents of the mind is truly a philosophical