Idealism is a foundational philosophical school of thought that posits reality is fundamentally mental or spiritual. It asserts that ideas and the mind are the ultimate reality, and the external world is either a manifestation of mind or dependent on consciousness for its existence.
The correct answer, B: Ideas and mind, accurately reflects this core tenet. Idealists believe that knowledge is primarily derived from introspection and reasoning, emphasizing the importance of concepts, thoughts, and the inner world.
A: Material world is incorrect because it aligns with materialism or realism, which hold that matter is the fundamental reality, independent of mind. C: Experience only is characteristic of empiricism, which emphasizes sensory experience as the sole source of knowledge, rather than the metaphysical nature of reality itself. While experience contributes to ideas, it's not the primary belief of idealism. D: Scientific method refers to a systematic approach to empirical investigation, which is a tool for understanding the material world, not a core belief about the nature of reality in idealism.