Arguably, the key task of developmental scientists is to describe and explain developmental change. Changes may occur within an individual across the life span, and there may be between-person differences in such intraindividual change. The description and explanation of intraindividual change involves the concepts of developmental continuity and discontinuity, whereas the description and explanation of interindividual differences in intraindividual change involves the concepts of stability and instability.
In regard to continuity and discontinuity, descriptions or explanations of development can involve quantitative or qualitative changes. Descriptively, quantitative changes involve differences in how much (or how many) of something exists. For example, in adolescence, quantitative changes occur in such areas as height and weight since there is an adolescent growth spurt, and these changes are often interpreted as resulting from quantitative increases in the production of growth-stimulating hormones.
In turn, descriptive qualitative changes involve differences in what exists, in what sort of phenomenon is present. The emergence in adolescence of a drive state never before present in life—that is, a reproductively mature sexual drive—and the emergence in adolescence of new and abstract thought capabilities not present in younger people—that is, in Jean Piaget’s terms, formal operations—are instances of changes interpreted as arising from qualitative alterations in the person. It is believed that the person is not just “more of the same”; rather, the person is seen as having a new quality or characteristic.
Explanations of development also can vary in regard to whether one accounts for change by positing quantitative changes (e.g., increases in the amounts of growth hormone present in the bloodstream) or by positing a new reason for behaviors (e.g., an infant’s interactions in his or her social world are predicated on the need to establish a sense of basic trust in the world, whereas an adolescent’s social interactions involve the need to establish a sense of identity, or a self-definition). In other words, it is possible to offer an explanatory discontinuous interpretation of development involving either quantitative or qualitative change.
For instance, when particular types of explanatory discontinuous qualitative changes are said to be involved in development, the critical periods hypothesis is often raised, as in Erik Erikson’s work. The point is that on the basis of adherence to a particular theory of development (e.g., what has been termed, in the scholarship of Gilbert Gottlieb, a predetermined epigenetic, or natural one), qualitative changes are believed to characterize ontogeny, and because of this, discontinuous explanations of change are needed.
Thus, virtually any statement about the character of intraindividual development involves, explicitly or implicitly, taking a position in regard to three dimensions of change: (1) descriptive continuity-discontinuity, (2) explanatory continuity-discontinuity, and (3) the quantitative versus the qualitative character of one’s descriptions and explanations—that is, the quantitative-qualitative dimension pertains to both description and explanation. In essence, then, one may have descriptive quantitative discontinuity coupled with explanatory qualitative continuity, or descriptive qualitative continuity coupled with explanatory quantitative discontinuity, and so forth.
For example, a feature of personality (e.g., a component of temperament, such as mood) may remain descriptively the same over time. It may be represented or depicted isomorphically at two different temporal points (e.g., positive mood may be represented by the percentage of facial expressions per unit time that are scored as indicative of smiling). Such cases therefore may be an instance of descriptive, qualitative continuity. However, more of this qualitatively invariant phenomenon may exist at time 2 (e.g., there may be more smiles per unit time), and thus descriptive quantitative discontinuity may be coupled with descriptive qualitative continuity.
Moreover, both descriptive quantitative discontinuity and descriptive qualitative continuity may be explained by the same ideas, such as by continuous explanatory principles. For example, smiling may be assumed to be released across life by biogenetically based physiological mechanisms. Alternatively, descriptive continuity or descriptive discontinuity may be explained by different ideas, such as by discontinuous explanatory principles. For instance, smiling may be assumed to be biogenetically released in early infancy and mediated by cognitively and socially textured processes across subsequent developmental periods. Indeed, if different explanations are, in fact, invoked, they may involve statements that constitute either quantitatively or qualitatively altered processes.
In short, the particular couplings that one posits as involved in human life will depend on the substantive domain of development one is studying (e.g., intelligence, motivation, personality, or peer group relations) and, as we shall see, primarily on one’s theory of development. That is, any particular description or explanation of intraindividual change is the result of a particular theoretical view of development. This implies that commitment to a theory that focuses only on certain variables or processes will restrict one’s view of the variety of changes that may characterize development. Indeed, theory, not data, is the major lens through which one “observes” continuity or discontinuity in development.
The Contributions Of Heinz Werner
Heinz Werner believed that considerable confusion existed among human developmentalists over the continuity-discontinuity issue and that at the crux of this confusion was a lack of understanding about two different aspects of change (i.e., quantitative and qualitative). He argued that these two aspects of change must always be considered in discussions of descriptive and explanatory continuity-discontinuity. However, Werner explained the superordinate conceptual importance of the qualitative-quantitative dimension of change.
Quantitative Change
In regard to the quantitative aspect of development, we have noted that there is change in a feature of development in regard to how much of something exists. Quantitative change is an alteration in the amount, frequency, magnitude, or amplitude of a developmental variable or process. For example, imagine that a person’s weight has been measured at the same time during each of his 8th through 13th years. He weighed 125 pounds when he was measured at 8, 9, 10, 11, and 12; but he weighed 150 pounds when he was measured at 13. Thus, a quantitative change occurred in how much weight existed between the times of measurement occurring at ages 12 and 13 years.
Alternatively, the child’s change in weight could have been gradual. By gaining 5 pounds per year, the child gradually goes from 125 to 150 pounds between his 8th and 13th years. With gradual quantitative changes, the rate of change stays the same—is continuous— from one measurement time to the next. This is quantitative continuity.
Thus, quantitative change may be abrupt. There are no intermediate steps by which the person’s weight gradually moved from one level (amount) to the next. In measuring this change, there is a gap between one point in the measurement curve and another; that is, a curve representing the different measurements is not smooth but has an abrupt change in its direction. There is a “gappiness” in the curve—a lack of an intermediate stage between the earlier and later levels of a variable. The occurrence of an abrupt change is quantitative discontinuity.
Qualitative Change
The second aspect of change that Werner specifies is the qualitative one. Here we are primarily concerned not with how much of something exists but with what exists—what kind or type of thing exists. Thus, we are concerned with whether or not a new quality has come to characterize an organism, whether something new has emerged in development. When we are considering qualitative change we are dealing with epigenesis, or emergence.
In distinguishing between quantitative and qualitative aspects of change, Werner highlights a core conception of the organismic position. Some of the types of changes that comprise development are emergent changes. These are changes in what exists rather than in how much of something exists. Something new comes about in development, and because it is new— because it is qualitatively different from what went before—it cannot be reduced to what went before. Hence, if at time 1 we can be represented by 10 oranges and at time 2 we can be represented by a motorcycle, we cannot reduce our time 2 motorcycle status to our time 1 orange status.
To take another example, before puberty a person may be characterized as being (in part) composed of several drives—for example, a hunger drive, a thirst drive, a drive to avoid pain, and perhaps a curiosity drive. With puberty, however, a new drive emerges (or, at least, emerges in a mature form)—the sex drive. With this emergence the adolescent begins to have new feelings, new thoughts, and even new behaviors which, according to Anna Freud, may be interpreted as being a consequence of this new drive. The emergence of this new drive is an instance of qualitative discontinuity. The sex drive cannot be reduced to hunger and thirst drives, for instance.
Hence, qualitative changes are by their very nature discontinuous. A qualitative, emergent, epigenetic change is always an instance of discontinuity. Moreover, not only is an emergent change an irreducible change, but it is a change characterized by gappiness. As indicated above, developmental gappiness occurs when there is a lack of an intermediate level between earlier and later levels of development. It should be clear that gappiness must also be a part of an emergent change. The presence of an intermediate step between what exists at time 1 and the new quality that emerges at time 2 would suggest that the new quality at time 2 could be reduced through reference to the intermediate step. Since we have just seen that an emergent change is defined in terms of its developmental irreducibility to what went before, it is clear that gappiness must also be a characteristic of any emergence.
Conclusions
The characteristics of emergence and gappiness are needed to describe qualitatively discontinuous changes in development; on the other hand, the characteristic of gappiness (abruptness) alone seems to suffice for characterizing quantitatively discontinuous changes. Thus, to quote Heinz Werner:
It seems that discontinuity in terms of qualitative changes can be best defined by two characteristics: “emergence,” i.e., the irreducibility of a later stage to an earlier; and “gappiness,” i.e., the lack of intermediate stages between earlier and later forms. Quantitative discontinuity on the other hand, appears to be sufficiently defined by the second characteristic.
. . . To facilitate distinction and alleviate confusion, I would suggest substituting “abruptness” for quantitative discontinuity, reserving the term “discontinuity” only for the qualitative aspect of change. (p. 133)
What Werner has provided us with, then, is a clarification of the concepts involved in appropriately considering the continuity-discontinuity issue. He has given us the conceptual means with which to discriminate between quantitative continuity-discontinuity and qualitative continuity-discontinuity in developmental change.
References:
- Erikson, H. (1959). Identity and the life-cycle. Psychological Issues, 1, 18–164.
- Gottlieb, G. (1997). Synthesizing nature-nurture: Prenatal roots of instinctive behavior. Mahwah, NJ:
- Lerner, R. M. (2002). Concepts and theories of human development (3rd ). Mahwah, NJ: Erlbaum.
- Piaget, J. (1972). Intellectual evolution from adolescence to adulthood. Human Development, 15, 1–12.
- Werner, (1957). The concept of development from a comparative and organismic point of view. In D. B. Harris (Ed.), The concept of development (pp. 125–148). Minneapolis: University of Minnesota Press.