The following is a metaphor I have presented to psychology trainees beginning last year to help them understand what ACT attempts to do and how it compares to a CBT approach. It has been very well received by the trainees, the vast majority of them coming into the program having had more exposure to CBT than to ACT.
This metaphor is based on an ACT definition of psychopathology, psychological inflexibility, which may not be how psychopathology is typically defined from a CBT approach. However, I think it is useful to think about how CBT techniques may be viewed from an ACT-based definition of psychopathology, especially as it helps demonstrate how ACT attempts to do something different than CBT.
Moving through the Maze of One's Thoughts and Feelings
Psychological inflexibility is the inability to adjust behavior on the basis of its usefulness in attaining desired ends, including not being able to change a behavior when change is needed and not being able to persist in a behavior when persistence is needed. This would be like being in a maze, where the walls consist of one's thoughts and feelings expanding infinitely in all directions, and having difficulty moving effectively about it, consistently and unproductively revisiting particular corners of the maze (rumination and worry) or being unable to successfully move around areas of the maze due to seeking to maintain distance from particular corridors of the maze (emotional and cognitive avoidance).
Given this definition of psychopathology, CBT techniques may be viewed as training in a variety of alternative behaviors. This would be like learning skills to help move around the maze: to become aware of how the different walls are linked together and what one typically does when they encounter particular walls (self-monitoring); to slowly retrace one's steps when they lead to a dead end and to see whether any openings were missed along the way (cognitive restructuring); to persist in walking down particular corridors (behavior activation), even uncomfortably narrow ones (tolerating negative affect), in order to reach different rooms (with walls consisting of positive affect, new beliefs regarding one's self-efficacy, new perspectives about the actual risk posed by a situation); and that by repeatedly persisting in walking uncomfortably narrow corridors without too quickly turning down more comfortable alternate hallways (exposure with response prevention) the narrow corridors begin to widen becoming more comfortable to walk through (habituation).
In contrast, ACT seeks to decrease the impact of the processes that lead to inflexibility. This would be like learning that where one goes in the maze does not have to be limited by its walls: that if one approaches a wall allowing oneself to come into full physical contact with it without resistance (acceptance), with openness and while maintaining awareness of one's five body senses (contact with the present moment), one can begin to notice that the walls are made of smoke (cognitive defusion), that it is possible to move into the walls without losing oneself inside of it (self-as-context), and walk through it (committed action) in whatever direction one chooses (values).
Thus, both approaches seek to assist people with moving about more effectively, though differ in how they attempt to create change.