In the book "A Bias for Action", which sets to differentiate willpower from motivation - the authors use the term volition as a synonym for willpower and describe briefly the theories of Kurt Lewin. While Lewin argues that motivation and volition are one and the same, the authors claim that Ach argues differently. According to the authors, Ach claims that there is a certain threshold of desire that distinguishes motivation from volition: when desire lies below this threshold, it is motivation, and when it crosses over, it becomes volition. Using this model, the authors consider individuals' differing levels of commitment with regard to tasks by measuring it on a scale of intent from motivation to volition. Modern writing on the role of volition, including discussions of impulse control (e.g., Kuhl and Heckhausen) and education (e.g., Corno), also make this distinction. Corno's model ties volition to the processes of self-regulated learning.