Final answer:
Trait theory is a modern theoretical approach to understanding personality, focusing on observable behavior and characteristics.
Step-by-step explanation:
The modern theoretical approach to understanding personality is Trait theory. Unlike psychoanalysis, behaviorism, and classical conditioning which focus on inner processes, Trait theory focuses on observable behavior. It seeks to identify and describe the stable patterns of behavior and characteristics that make up an individual's personality, such as introversion, extroversion, or agreeableness.