"Before moving on to consider the details involved in identifying Bombadil as a nature spirit, it is helpful to get a better understanding of nature spirits in general. As it turns out, it is more straightforward to collect evidence that Goldberry is such a being, which would be a natural corollary if Tom had that identity, so we will begin with her. One of the strongest statements supporting this identity for Goldberry comes from Letter #210, in which Tolkien speaks of her and says "We are not in 'fairy-land', but in real river-lands in autumn. Goldberry represents the actual seasonal changes in such lands." This letter, written after the completion of LotR, indicates that at least in some sense Tolkien saw Goldberry as a nature spirit, specifically a spirit associated with river-lands and seasons."
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