The paper introduces to second language researchers the
microgenetic method emerging in cognitive psychology. Over the past
twenty years, an increasing number of researchers have adopted this method to study the path and mechanism of change in cognitive development with a focus on variability within a group and within a subject. The method is characterized by three essential properties: a sufficiently long observation span, a high density of observations and an intensive analysis of the observation data. It can distinguish among five dimensions of change: its path, rate, breath, source and variability. The path of change refers to the sequence of knowledge states or problem -solving strategies when the subjects are gaining competence whereas the rate of change specifies the period of time that separates the initial discovery of a new strategy from the consistent use of it. While the breadth of change shows how widely the strategy consistently used in the treatment is generalized to other problems and contexts, the source of change involves the causes that set the change in motion. The last dimension of change, i. e. the variability, measures how subjects in an experiment differ from one another in terms of path, rate, breadth and source of change. The most outstanding feature of this method is that it can be used to do research on diversified cor hent areas and populations, and can make up for some of the limitations of cross - sectional and longitudinal studies. However, it is difficult to use this method extensively because it is time - consuming and labor - intensive, and it requires the subjects to be well motivated and extremely cooperative. The paper finally explores the possibilities of using this method in doing research on
second language acquisition. It suggests that we may use this method to investigate frequency effects on the correction of students' fossilized errors or the learning of a new linguistic item. The findings yielded by this method will reveal the mechanism of change in L2 development and the complexities of L2 learning.