The paper discusses the hypothesis that capacity for differentiation is a precondition for construction of a new action. A study was conducted with the aim of testing the hypothesis. Visual feed-back was delayed to achieve disruption of an action being performed. The data show that when visual control of an action is disrupted, the motor component begins to play the leading role. A whole purposeful action turns into a series of consecutive movements alternating with pauses. The pauses are necessary for evaluation, control and planning of the next movement. These pauses are the "leading force" for the construction of a new action in new complicated conditions. The inner, hidden structure of an action opens itself to observation and research, becomes perceivable to the subject due to its capacity for disclosing itself when the outside situation changes. This capacity for differentiation creates conditions for construction of a new action, it enables the subject to overcome negative consequences caused by disruption or replacement of the outside means of activity and to form an action adequate to new conditions.