Front Page Titles (by Subject) PREFACE. - The Principles of Psychology
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PREFACE. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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The four parts of which this work consists, though intimately related to each other as different views of the same great aggregate of phenomena, are yet, in the main, severally independent and complete in themselves. The particular serial arrangement in which they should be presented, has consequently been in great measure a question of general expediency; and while the order I have chosen is one which seems, on the whole, the most advantageous, it is not one which all readers are bound to follow. A brief characterization of each part, will enable every one to decide for himself which he may best commence with.
The General Analysis (of which the essential portion was originally published in the Westminster Review for October, 1853, under the title of “The Universal Postulate,” and reappears here with additional arguments and explanations) is an inquiry concerning the basis of our intelligence. Its object is to ascertain the fundamental peculiarity of all modes of consciousness constituting knowledge proper—knowledge of the highest validity.
The Special Analysis has for its aim, to resolve each species of cognition into its components. Commencing with the most involved ones, it seeks by successive decompositions to reduce cognitions of every order to those of the simplest kind; and so, finally to make apparent the common nature of all thought, and disclose its ultimate constituents.
While these analytical parts deal with the phenomena of intelligence subjectively, and, as a necessary consequence, are confined to human intelligence; the synthetical parts deal with the phenomena of intelligence objectively, and so include not human intelligence only, but intelligence under every form.
The General Synthesis, setting out with an abstract statement of the relation subsisting between every living organism and the external world, and arguing that all vital actions whatever, mental and bodily, must be expressible in terms of this relation; proceeds to formulate, in such terms, the successive phases of progressing Life, considered apart from our conventional classifications of them.
And the Special Synthesis, after exhibiting that gradual differentiation of the psychical from the physical life which accompanies the evolution of Life in general, goes on to develop, in its application to psychical life in particular, the doctrine which the previous part sets forth: describing the nature and genesis of the different modes of Intelligence, in terms of the relation which obtains between inner and outer phenomena.
As may be supposed, the analytical divisions are much less readable than the synthetical ones. Hence, while all who are accustomed to studies of an abstract character are recommended to follow the order in which the parts stand, as being that most conducive to a clear understanding of the system in its ensemble; those who are unfamiliar with mental philosophy may, perhaps, more advantageously begin with Parts III. and IV: returning to Parts I. and II. should they feel sufficiently interested to do so.
Respecting the execution of the work, I may say that in sundry ways it falls much short of my wishes. There are places in which the argument is incompletely carried out; places in which, from inadequate explanation, there is an apparent incongruity between the statements there made and those made elsewhere; and there are, I fear, places where the form of expression is not so precise as it should be. Add to which, that in treating under several separate aspects a subject so extensive, I have perhaps erred in attempting too much; and have so devoted neither thought enough nor space enough to any one of the several aspects under which the subject is presented.
While, however, I am conscious that the work contains many more imperfections than it would have done had its scope been more limited and its elaboration longer, I would excuse the issue of it in its present form on several grounds: partly on the ground that it is almost useless to wait until any organized body of thought has reached its full development, which it never does in the course of a single life; partly on the ground that it is next to impossible for the writer of a work like this, to dispense with the aid of candid criticism; but chiefly on the ground that the general truths enunciated, being, as I believe, both new and important, it seemed to me undesirable to delay their publication with the view of by and by presenting them in a more finished guise.
For the somewhat abrupt termination of the work, my apology must be, that disturbed health has obliged me to desist from writing a “Summary and Conclusion,” in which I purposed to bring the several lines of argument to a focus. I greatly regret this; not only because the harmony that may be shown to subsist between the doctrines elaborated in the respective divisions, is a strong confirmation of their truth; but because, in the absence of explanation, some misunderstanding may arise concerning the implications—ontological and other—which many will think manifest.
It may be well further to say, that, originally, I had intended to add a fifth division, which should include sundry deductions and speculations that could not properly be embodied in the other divisions. But before being compelled to do so, I had decided, that as this fifth division was not strictly necessary; and as certain of the suggestions contained in it might prejudice some against the doctrines developed in the others; it would be better to withhold it—at any rate for the present.