How did sensation and reflection provide the materials for knowledge in John Locke’s philosophy?

In his An Essay Concerning Human Understanding, John Locke rejected the doctrine of innate ideas, arguing instead that the human mind begins as a tabula rasa, or blank slate. He posited that all materials for knowledge are derived from two primary sources:

• Sensation: This is the process by which the mind receives sensory impressions from the external world, such as the color of a rose, the taste of salt, or the sound of a bell.12
• Reflection: This is the mind’s internal awareness of its own operations, such as thinking, doubting, believing, or experiencing emotions like happiness or sadness.12

Locke termed these materials "ideas," which serve as objects before the mind. While sensation and reflection provide the raw "simple ideas," the mind acts as an agent that compounds and combines these into "complex ideas". Through this process of sensory atomism, Locke sought to explain the origin of all human conceptual experience, moving from simple sensory building blocks toward complex understanding.13