Thoreau develops his themes in Walden primarily through figurative language, rather than symbolism. Frequently, he develops analogies. Ideas are communicated by comparing one thing to another and then explaining how they are alike. For instance, consider this passage:
It is remarkable how easily and insensibly we fall into a particular route, and make a beaten track for ourselves. I had not lived there a week before my feet wore a path from my door to the pond side; and thought it is five or six years since I trod it, it is still quite distinct. It is true, I fear that others may have fallen into it, and so helped to keep it open. The surface of the earth is soft and impressible by the feet of men; and so with the paths which the mind travels. How worn and dusty, then, must be the highways of the world, how deep the ruts of tradition and conformity!
In comparing the well worn path to the minds of men, Thoreau makes the point that falling into tradition and conformity, without thinking, is quite easy and not to be desired. When removed from the analogy, a worn path can be symbolic of conforming to tradition without thinking independently.
In a following passage, Thoreau makes this statement:
I did not wish to take a cabin passage, but rather to go before the mast and on the deck of the world, for there I could best see the moonlight amid the mountains. I do not wish to go below now.
In this passage, Thoreau does not develop an analogy, but instead develops an implied metaphor. Taking a sea voyage is indirectly compared to living one's life. It can be done independently and adventurously or traditionally and safely. Within the metaphor, living adventurously "on the deck of the world" is more enriching for the spirit.
Rather than developing a few central symbols within Walden, Thoreau communicates his Transcendental themes through figures of speech that appear frequently throughout the work.