Change, Quantitative and Qualitative Aspects of

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 areas as such 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 (Freud, 1969)—and of new and abstract thought capabilities not present in younger people—that is, formal operations (Piaget, 1950, 1972)—are instances of changes interpreted as arising from qualitative alterations in the person. It is [Page 231]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 can vary also in regard to whether one accounts for change by positing quantitative changes (for example, 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 (e.g., Erikson, 1959, 1964). The point is that on the basis of adherence to a particular theory of development (e.g., predetermined epigenetic, or nature; Gottlieb, 1997), 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.

...