The philosophic foundation of Adlerian psychotherapy lies in its dialectical understanding of the soul in the world. This is expressed by Gustav Emil Mueller, who probably had no connection with Adler or his movement, in his book Dialectic: a way into and within philosophy.
An action is always perceived as being purposive. It is characterised by meaning or intending something beyond itself. Tell me what you believe in, what you strive for, and I can tell you what you are. An action begins with a feeling of discrepancy between my wishes and the situation. If my wishes are frustrated by an obstacle I am compelled to take a look, to form a clearer perception of the obstacle, whereupon I build my plans to remove or alter the obstacle in order to suit my desire. … The soul is perceived in its actions as individuated. Individual means unique and indivisible. You cannot separate any action of feeling, desire, thinking, dreaming, and so forth, from the self which is inseparable from them as their unity.