American life is a powerful solvent. It seems to neutralize every intellectual element, however tough and alien it may be, and to fuse it in the native good will, complacency, thoughtlessness, and optimism.

Calling American life a “powerful solvent” suggests an assimilative culture that dissolves sharp distinctions. Santayana implies that complex or “alien” intellectual traditions—skeptical, tragic, metaphysical, or aristocratic—are softened when they enter an environment dominated by good will, practical complacency, and buoyant optimism. The fusion he describes is not necessarily praise: “thoughtlessness” hints that the process can flatten depth and critical rigor, turning ideas into agreeable attitudes. At the same time, the passage acknowledges America’s remarkable integrative power: it can incorporate difference without constant ideological conflict, though often at the cost of intellectual edge and historical consciousness.