**Core Concept:** The structural theory of mind refers to the belief that the mind is composed of distinct mental entities or substances, each with its own structure and function. This concept was proposed by French philosopher René Descartes in the 17th century.

**Why the Correct Answer is Right:** René Descartes, a prominent figure in the history of Western philosophy, developed the structural theory of mind. In this theory, Descartes proposed that the mind consists of separate components or substances, each with its own distinct structure and function. This idea is significant because it laid the foundation for the subsequent development of cognitive psychology and neuroscience research.

**Why Each Wrong Option is Incorrect:**

A. **The American psychologist William James**: While William James is known for his contributions to psychology, particularly the concept of consciousness, he did not propose the structural theory of mind.

B. **The German philosopher Immanuel Kant**: Immanuel Kant is most renowned for his critique of pure reason and the Categorical Imperative, not the structural theory of mind.

C. **The English philosopher John Locke**: John Locke is known for his ideas on empiricism and the doctrine of the internal sense, not the structural theory of mind.

D. **The Italian philosopher Giovanni B. Moretti**: Giovanni B. Moretti is primarily associated with philosophical and political works, not the structural theory of mind.

**Clinical Pearl / High-Yield Fact:** A prominent example of the structural theory of mind is the distinction between the conscious and unconscious mind. This principle has influenced the development of modern neuroscience and has contributed to our understanding of the relationship between mental processes and brain functions.