The doctrine that correlatives imply one another —that a father cannot be thought of without thinking of a child, and that there can be no consciousness of superior without a consciousness of inferior—has for one of its common examples the necessary connexion between the conceptions of whole and part. Beyond the primary truth that no idea of a whole can be framed without a nascent idea of parts constituting it, and that no idea of a part can be framed without a nascent idea of some whole to which it belongs, there is the secondary truth that there can be no correct idea of a part without a correct idea of the correlative whole. There are several ways in which inadequate knowledge of the one involves inadequate knowledge of the other. (§1 ¶1)

If the part is conceived without any reference to the whole, it becomes itself a whole—an independent entity; and its relations to existence in general are misapprehended. Further, the size of the part as compared with the size of the whole, must be misapprehended unless the whole is not only recognized as including it, but is figured in its total extent. And again, the position which the part occupies in relation to other parts, cannot be rightly conceived unless there is some conception of the whole in its distribution as well as in its amount. (§1 ¶2)

Still more when part and whole, instead of being statically related only, are dynamically related, must there be a general understanding of the whole before the part can be understood. By a savage who has never seen a vehicle, no idea can be formed of the use and action of a wheel. To the unsymmetrically-pierced disk of an eccentric, no place or purpose can be ascribed by a rustic unacquainted with machinery. Even a mechanician, if he has never looked into a piano, will, if shown a damper, be unable to conceive its function or relative value. (§1 ¶3)

Most of all, however, where the whole is organic, does complete comprehension of a part imply extensive comprehension of the whole. Suppose a being ignorant of the human body to find a detached arm. If not misconceived by him as a supposed whole, instead of being conceived as a part, still its relations to other parts, and its structure, would be wholly inexplicable. Admitting that the co-operation of its bones and muscles might be divined, yet no thought could be framed of the share taken by the arm in the actions of the unknown whole it belonged to; nor could any interpretation be put upon the nerves and vessels ramifying through it, which severally refer to certain central organs. A theory of the structure of the arm implies a theory of the structure of the body at large. (§1 ¶4)

And this truth holds not of material aggregates only, but of immaterial aggregates—aggregated motions, deeds, thoughts, words. The Moon’s movements cannot be fully interpreted without taking into account the movements of the Solar System at large. The process of loading a gun is meaningless until the subsequent actions performed with the gun are known. A fragment of a sentence, if not unintelligible, is wrongly interpreted in the absence of the remainder. Cut off its beginning and end, and the rest of a demonstration proves nothing. Evidence given by a plaintiff often misleads until the evidence which the defendant produces is joined with it. (§1 ¶5)