In the many different veins of cognitive development research, certain themes and assumptions seem to run throughout. Most of the background beliefs common to the field are truly taken for granted to such an extent that they become largely unspoken and perhaps never even considered. For example, most cognitive research theory assumes without question the theory of human minds which claims that ones fellow humans are not automata but that one can look at their actions and listen to their words and from their gain a relatively accurate image of the mind which is producing these phenomena of movement and speech. This seems obvious to cognitive researchers, but is much in debate among philosophers. Many other such basic assumptions are taken for granted, such as the idea that children actually learn and progress from a relatively blank state, rather than (as Plato and others such as Wordsworth have suggested) entering the world "trailing clouds of glory" and past memories and perceptions which are recalled rather than discovered. With such a broad base of common assumptions, the slight variations in assumptions between the different veins of cognitive development may seem more trivial. Nonetheless it is difficult to truly identify -- across the board -- what one would call the primary assumptions and propositions of cognitive development theory, as these do vary from case to case.
Some of the more foundational assumptions for many schools of cognitive development theory are those which claim that growth and development take place in recognizable stages, and the question is only how to define those stages. This assumption is linked to the idea that growth develops from the simple to the complex linearly, with each stage setting the foundation for the next and being integrated into it. Varying schools of theory will argue about the assumed way in which people change and the nature of this change, whether it is active or reactive, internally or externally motivated, and based on continuity or discontinuity. Stage theories tend to assume active and reactive learning, but say that development is based on qualitative change and the discontinuity of development, and that biological maturation is a primary influence. Learning theorists, on the other hand, assume a continuity of development characterized by stability, and speculate that change is quantitative and based on experience and environment. So one can see that assumptions are not quite the same across the field of cognitive research, and may actually be somewhat opposite in nature. Some of the differences in theory and even in the results of the various approaches to cognitive research may stem from these differences in the basic assumptions made before research is done.
The difference that assumptions can make in the research findings of cognitive development is evident if one compares and contrasts the findings of Piaget and Bruner. These two have rather different basic assumptions and different ways of defining central terms, which have led to differences in their focus and in their conception of the stages of development. Piaget's theory was centered on the linear development of cognition as the child progressed from infancy into adulthood. He spoke of cognitive development as a sort of continual movement from one distinct stage to another, and indicated that at each stage the mental processes were uniquely different. Progress was made between stages when children experienced discrepancies between prior knowledge and knew experiences. This created a sort of disequilibrium that destroyed the old stage and ushered in a new one. As Piaget defined it, then, cognition was based on an understanding of the world and its classifications, whether that be through mental representation or more abstract thought. Stages were defined by shifts in the way cognition was performed, and maintained a relatively strong set of boundaries between them. Specific stages were generally associated with periods (ages) in a child's life which were generally progressive and led naturally one into the other.
For Bruner, on the other hand, the theory was centered on the way in which individual cognition --or understandings-- were formed. He focused more on learning as the outcome of cognitive development, rather than on cognitive development as independent from learning. He seemed to assume that children were not inherently different from adults in their approach to learning. Both children learning about life for the first time and adults approaching new situations would, according to Bruner's ideas, go through…