1. We have as many laws of psychical development as we had principles of psychical causality, and the former may be regarded as the application of the latter to more comprehensive psychical interconnections. We designate the laws of development as laws first of mental growth, second of heterogony of ends, and third of development toward opposites.

2. The law of mental growth is as little applicable to all contents of psychical experience as is any other law of psychical development. It holds only under the limiting condition which applies to the principle of resultants, the application of which it is, namely the condition of the continuity of the processes (p. 369). But since the circumstances that tend to prevent the realization of this condition, are, of course, much more frequent when the mental developments concerned include a greater number of psychical syntheses, than in the case of the single syntheses themselves, it follows that the law of mental growth can be demonstrated only for certain developments taking place under normal conditions, and even here only within certain limits. Within these limits, however, the more comprehensive developments, as for example the mental development of the normal individual and the development of mental communities, are obviously the best exemplifications of the fundamental principle of resultants, which principle lies at the basis of this development.

3. The law of heterogony of ends is most closely connected with the principle of relations, but it is also based on the principle of resultants, which latter is always to be taken into consideration when dealing with the larger interconnections of psychical development. In fact, we may regard this law of heterogony of ends as a principle of development which controls the changes arising as results of successive creative syntheses, in the relations between the single partial contents of psychical compounds. The resultants arising from united psychical processes include contents which were not present in the components, and these new contents may in turn enter into relation with the old components, thus changing again the relations between these old components and consequently changing the new resultants which arise. This principle of continually changing relations is most strikingly illustrated when an idea of ends is formed on the basis of the given relations. In such cases the relation of the single factors to one another is regarded as an interconnection of means, which interconnection has for its end the product arising from the interconnection. The relation in such a case between the actual effects and the ideated ends, is such that secondary effects always arise which were not thought of in the first ideas of end. These new effects enter into new series of motives, and thus modify the earlier ends or add new ends to those which existed at first.

The law of heterogony of ends in its broadest sense dominates all psychical processes. In the special teleological coloring which has given it its name, however, it is to be found primarily in the sphere of volitional processes, for here the ideas of end together with their affective motives are of the chief importance. Of the various spheres of applied psychology, it is especially ethics for which this law is of great importance.

4. The law of development towards opposites is an application of the principle of intensification through contrast, to more comprehensive interconnections which form in themselves series of developments. In such series of developments there is a constant play of contrasting feelings in accordance with the fundamental principle of contrasts. First, certain feelings and impulses of small intensity begin to arise. Through contrast with the predominating feelings this rising group increases in intensity until finally it gains the complete ascendency. This ascendency is retained for a time and then from this point on the same alternation may be, once, or even several times, repeated. But generally the laws of mental growth and heterogony of ends operate in the case of such an oscillation, so that succeeding phases, though they are like corresponding antecedent phases in their general affective direction, yet differ essentially in their special components.

The law of development towards opposites shows itself in the mental development of the individual, partly in a purely individual way within shorter periods of time, and partly in certain universal regularities in the relation of various periods of life. It has long been recognized that the predominating temperaments of different periods of life present certain contrasts. Thus, the light, sanguine excitability of childhood, which is seldom more than superficial, is followed by the slower but more retentive temperament of youth with its frequent touch of melancholy. Then comes manhood with its mature character, generally quick and active in decision and execution, and last of all, old age with its leaning towards contemplative quiet. Even more than in the individual does this principle of development towards opposites find expression in the alternation of mental tendencies which appear in social and historical life, and in the reactions of these mental tendencies on civilization and customs and on social and political development. As the law of heterogony of ends applied chiefly to the domain of moral life, so this law of development towards opposites finds its chief significance in the more general sphere of historical life.