Abstract: Taking the two early philosophical papers of Charles S. Peirce as clues of research, this essay shall analyze and discuss some basic ideas of the classical American pragmatism, such as “living doubt” “the fixation of belief” “thought as inquiry” “scientific method and reality” and “fallibilism”, etc., Thought as the fixation of belief or the inquiry of knowledge is no longer a process of mere theoretical comprehension, but more of scientific inquiring procedure or steps for raising and solving problems. This investigation and analysis shall explore how the “American philosophy” has been transformed from “an European philosophy in the USA” to “a philosophy from the USA” as pragmatism. This pragmatism has become the philosophical foundation of what was later called the “American Spirit,” and the starting point of the flourishing 20th-century American philosophy.