Projective tests are based on the assumption that

Projective tests are based on the assumption that abmiguous and unstructured personality stimuli can trigger significant data about a persons personality and psychological traits to structure a personality type based on the information provided and the association information psychologist have in their theories.  

Explanation:

Ok, to understand why projective tests are based on the assumption that ambiguous and unstructured stimuli would trigger personality significant data to identify their personality type and traits we have to understand what they are.

Well, projective tests are psychological tests based on different theories, the majority of them humanistic, psychodynamic and cognitive. They establish associations between those theories and subjects' performance under a certain instruction. So, the experts creating them run a great number of tests, then they identify the subjects personality type from other sources of personality explorations and then they associate the type of response they execute to their corresponding personality type, trait or behavioral pattern to classify it as a generalization response from the population with a certain psychological trait, characteristic or behavioral pattern.

answer; analytical,creative and practical;