American Psychologist who made significant contributions to  the development of   modern psychology

One of the most influential American psychologists who made significant contributions to the development of modern psychology is William James.

Step 1: Identify the Psychologist William James is a renowned psychologist from America. He was born on January 11, 1842, and died on August 26, 1910.

Step 2: Understand His Contributions James is often referred to as the father of American psychology. His ideas and theories have had a profound impact on psychology as we know it today. He was the first to offer a psychology course in the United States and his teaching and writing helped shape the growth of psychology in America.

Step 3: Highlight Key Theories One of his most significant contributions is his theory of pragmatism. This theory suggests that the truth of an idea can never be proven, but is instead determined by its usefulness in helping people to adapt and survive.

Step 4: Discuss His Influence James' work has influenced a number of different areas within psychology, including functionalism and educational psychology. His ideas have also had a significant impact on various fields outside of psychology, such as philosophy and religion.

In conclusion, William James' contributions to psychology have been instrumental in shaping the field as we know it today. His theories and ideas continue to influence and inspire psychologists around the world.