The doctrine that correlatives imply one another has, for one of its common examples, the relation 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. Still less, when part and whole are dynamically related, and least of all when the whole is organic, can the part be understood except by comprehension of the whole to which it belongs. This truth holds not only of material but also of immaterial aggregates. Conduct is a whole and, in a sense, an organic whole, and Ethics, of which it is a part, cannot be understood except through the understanding of the whole of conduct. A definition of conduct must exclude purposeless actions,--such, for instance, as those of an epileptic in a fit. Hence the definition emerges either: acts adjusted to ends; or, the adjustment of acts to ends; according as we contemplate the formed body of acts, or think of the form alone. And conduct, in its full acceptation, must be taken as comprehending all adjustments of acts to ends, from the simplest to the most complex, whatever their special natures and whether they are considered separately or in their totality. A large part of conduct is non-ethical, indifferent; this passes, by small degrees and in countless ways, into conduct which is either moral or immoral. The acts of all living creatures, as acts adjusted to ends, come within the definition of conduct; the conduct of the higher animals as compared with that of man, and of the lower animals as compared with the higher, differs mainly in that the adjustments of acts to ends is relatively simple and relatively incomplete. And as in other cases, so in this case, we must interpret the more developed by the less developed; human conduct as a part of the whole of the conduct of animate beings. And further: as, in order to understand the part of human conduct with which Ethics is concerned, we must study it as a part of human conduct as a whole, and in order to understand human conduct, we must again study it as a part of the whole of conduct exhibited in animate beings, so, in order to comprehend this too, we must regard it as an outcome of former, less developed conduct, out of which it has arisen. Our first step must be to study the evolution of conduct. Morphology deals with physical structure, physiology with the processes carried on in the body. But we enter on the subject of conduct when we begin to study such combinations among the actions of sensory and motor-organs as are externally manifested.