Space, Place, Sign, and Symbol

I am reading Yi-Fu Tuan's very clearly written, Space and Place: The Perspective of Experience. In his chapter on "Architectural Space and Awareness," which ranges from China, ancient Sumer, medieval European Cathedrals to modern architecture, he discusses the symbolic importance of space in a larger coherent worldview that is reflected in how we build, whether a home, a village, a church, or a skyscraper. While much of the chapter emphasizes continuities in how each society constructs its buildings and shelters in relationship to its larger symbolic system (to borrow a phrase from Mary Douglas), he notes something different is now happening in the modern world. Firstly, because of the high rates of literacy, the use of material and physical symbols are fading as the importance of verbal symbols rise: "verbal symbols have progressively displaced material symbols, and books rather than buildings instruct" (117). But there is something more, or something less that is happening. Symbols are themselves being emptied of their potency to organize the world because of a fractured worldview in modern perspective:

Symbols themselves have lost much of their power to reverberate in the mind and feeling since this power depends on the existence of a coherent world. Without such a world symbols tend to become indistinguishable from signs. (117)

How is Tuan differentiating between sign and symbol? It seems that he sees symbols as meaningful in and of themselves even as they indicate something else, whereas signs can only indicate something else. Or, perhaps in religious terms, symbols participate in the qualities of what they point toward, whereas signs may not. Symbols belong to a set of other symbols in a relatively closed (coherent) system; signs can exist outside such a system.