What possible themes are established at the beginning of chapter five in Lord of the Flies?

A good way to identify themes, especially in brief excerpts, is to look for patterns. In the opening of chapter five, there is considerable description of the place where Ralph walks, how he walks, and what he thinks about while walking. After identifying this pattern of physical behavior, we need to consider the relationship of the character's physical actions to his mindset. By doing so, we can see that walking reflects Ralph's newfound maturity, a theme that is assisted by a more subtle theme of choice. 

We are told that there is “only a narrow strip of firm beach” which Ralph chooses “because he needed to think, and only here could he allow his feet to move without having to watch them.” Ralph believes he needs to be completely free from distraction to make decisions, yet by choosing such a path he shows that he is already capable of making a decision. This realization comes to him as “suddenly, pacing by the water, he was overcome with astonishment. He found himself understanding the wearisomeness of this life, where every path was an improvisation and a considerable part of one’s waking life was spent watching one’s feet.” Ralph’s newfound awareness of “every path” as an “improvisation” shows that he now understands that decisions must often be made without reflection. “Watching one’s feet,” then, acknowledges the circumstances that accompany those decisions while accepting the consequences that follow, whether or not they were intended.  

Such a realization shows that Ralph’s new awareness of decision making ushers him towards the “wearisomeness” of an adult life fraught with choices. This is further evidenced when he consciously quits walking to reflect: “He stopped, facing the strip; and remembering that first enthusiastic exploration as though it were part of a brighter childhood, he smiled jeeringly.” The physical act of stopping in the present marks his ability to reflect upon the past, suggesting that the emphasis on decision is related to Ralph’s body and mind maturing. He distinguishes his remembrance of his earlier walk as childish, an “enthusiastic exploration” because his decisions were not accompanied by any responsibilities. This is a major contrast to his decisions now, which he understands as “wearisomeness.” He also smiles “jeeringly,” mockingly, at his younger self, which mimics how adults often view the foolish naivety of their youth.

Thus, chapter five's opening themes of choice and consequence assist one of the book’s primary themes: Ralph’s loss of innocence. The reader is further reminded of this overall theme as the opening paragraph of chapter five ends: Ralph thinks that “there must be no mistake about this assembly, no chasing imaginary …” The repetition of the word “no” shows that Ralph is committed to a course of action, one that disregards the “imaginary” realm of youth and accepts responsibility. He is decisive, assertive, and willing to face consequences, completing the theme of choice that assists his development.

Of course, this is only partway through the book and that larger theme is also still maturing, so the second paragraph of chapter five immediately contrasts the chapter’s opening as Ralph is once again “lost … in a maze of thoughts.” Thus, we can see that Ralph’s coming-of-age is not entirely finished, and it will continue to progress during the rest of the novel.