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How did John Locke explain the formation of complex ideas?

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Painting by Joseph Aubert of Saint Thomas Aquinas seated with a book, wearing a halo and black and white robes, surrounded by ornate patterns in St. Stephens Church, Jerusalem. — Western philosophy Painting of scholastic philosopher St. Thomas of Aquinas by Joseph Aubert, 1900.

In his seminal work, An Essay Concerning Human Understanding, John Locke argued that the human mind begins as a blank slate, or tabula rasa, and that all knowledge is derived from experience through sensation and reflection.123

Locke categorized all ideas as either simple or complex. Simple ideas are the basic materials of knowledge, received passively by the mind through sense experience (such as the color or texture of an object) or internal reflection (such as the awareness of one's own thinking).243

Complex ideas are formed through the active mental process of "compounding," where the mind combines, repeats, or compares these simple ideas. For example, the complex idea of an apple is constructed by bringing together simple ideas of its color, shape, texture, and taste. Furthermore, Locke explained that general ideas are formed through the process of abstraction, where the mind strips away the specific qualities of particular things to identify common characteristics.2435