Change that is continuous, and which follows certain trends over time (e.g., asymptotic, exponential, logistic, monotonic) is considered to be quantitative. Appositional growth is a good example of this type of change. Allometric growth is an example of qualitative change, with metamorphosis being its most extreme expression. It not only signifies changes in form and function, but also the emergence of new properties via transitional periods of reorganisation. The problem here is to know when a qualitative change represents something really new. Catastrophe theory has developed a number of signifiers (termed ‘flags’) for detecting such evidence. The distinction between ‘quantitative’ and ‘qualitative’ and between ‘continuous’ and ‘discontinuous’ are abstractions from reality as both forms of change interrelate during both growth and ontogenetic development. Thus, quantitative change at one level of the system (referred to as the ‘micro-level’ by physicists) can, when it exceeds some critical value, bring about a discontinuous qualitative transformation at another level (the macro-level).
See Allometry, Balance scale task, Bifurcation, Catastrophe theory, Control parameter, Developmental bootstrapping, Emergence, Growth, Hysteresis, Dissipative system, Order parameter, Metamorphosis (or indirect development), Ontogenetic adaptation, Open system, Progress, Quantitative and quantitative change, Quantitative and qualitative regressions