Faith vs. Doubt
Verne wanted to show the difference between faith and doubt, and explored exactly this theme through his characters. Professor Lidenbrock exhibits eternal faith from the beginning of the story, when he is positive that he will decipher the parchment. Despite trying for days to decode the document, he never gives up. When he finally deciphers it, he insists on going to the volcano indicated by this document despite the fact that such a volcano is dangerous and might erupt at any time. Ultimately, Lidenbrock had faith that what was written was original and right. Axel, in contrast, is always skeptical. He tries his best to persuade his uncle to stop the journey, yet finds that his efforts are futile. Even in the middle of the journey, he consistently fears death. When Axel and his companions are involved in dire situations, Axel always assumes that they have reached their doom. Nevertheless, his uncle unflaggingly believes that they can get out of trouble one way or another. In the end, faith wins, and the explorers return safely to their homeland.
Man vs. Nature
Throughout the novel, Lidenbrock is both an observer and a rival of Nature. He has a scientist's appreciation for the natural world, and most of the time does not deliberately try to alter or destroy it. However, it is clear that he is no mere passive observer; after all, his goal of reaching the center of the Earth takes priority over unequivocal support and respect for Nature herself. In fact, occasionally Lidenbrock is quite dismissive of Nature, blithely assuming that she will provide for him and his companions when she has no reason to, and ignoring the ominous signs and warnings that she sets in their path. When the ultimate obstacle to their progress—the rock—reveals itself, Lidenbrock grants his approval to blow it up regardless of the consequences. Not long before, he had wildly boasted that he would beat Nature. Unfortunately for him, Nature has the last laugh, literally expelling him from her insides through a volcanic eruption.
Survival
While much of Verne's depicted journey is awe-inspiring yet fairly safe, at other times it is incredibly dangerous and requires more of the travelers than note-taking and walking. In fact, Nature is at her most primitive beneath the Earth, and these human beings must necessarily adapt themselves to her. Water is not a given, tempestuous storms rage and destroy, fearsome beasts emerge, the wind takes the expedition off course, and the dark is heavy and lonely. There are several points along the journey at which Axel and his companions actually come close to perishing; Axel's finding himself lost and alone is one of the more terrifying episodes. Overall, this journey requires of its participants that they be willing to sacrifice almost everything—perhaps even their lives—to complete it.
Time and Space
Not only do the travelers move through space, descending down into the depths of the planet, but they also move through time. Verne desires to show his readers the successive levels of human and biological history, giving us a veritable paleontological, geological, and anthropological lesson. This authorial choice allows Verne to fuse literature and science even as he transcends the boundaries of both.
Science vs. Fiction
Journey to the Center of the Earth is certainly a novel in many respects: there are a structured plot, fictionalized characters, carefully-orchestrated narrative devices, and fantastical elements. However, Verne's composition defies many 19th-century novelistic tendencies in its fixation on numbers, runes, facts, data, and long-winded accounts of scientific findings. There are many passages that are incredibly didactic or tangential, and sometimes these passages threaten to overtake the main narrative. Thus, Verne is fusing two genres or disciplines; his work is a novel, but it is in another sense his attempt to lay plain the scientific realities of his day. He delights in both topics and the novel (mostly) excels in examining both. It is both science and fiction as well as, of course, classic science fiction.
Knowledge and Discovery
Verne's novel glories in the pursuit of knowledge in its purest form. Both Lidenbrock and Axel exhibit a pure, almost childlike glee in the study of their field. The first time we are introduced to Lidenbrock, he is aflame with enthusiasm over Turleson's manuscript. Such intellectual curiosity sustains these men throughout their arduous journey; even Axel's anxiety and trepidation are often quelled by the fervor of discovery. The things they witness below the surface of the Earth are things that no one else (except Saknussemm, putatively) has ever seen, and Verne depicts the characters' stunned reactions in a memorable and believable way. Despite their distance from us in terms of their fictional status, Verne's creations are stand-ins for readers who would no doubt be just as thrilled to see a plesiosaurus, a 12-foot-tall man, or a mastodon.
Courage
Courage manifests itself in many ways in the narrative. Hans's courage is quiet, unbending. He keeps any fears to himself; he knows that it is his job to be on the expedition and he exhibits the courage that this duty requires. Lidenbrock's courage is also unbending but is almost foolhardy, boisterous. He projects it outward, most likely to convince himself and Axel that they are on the right course; after all, his courage stems from his fervent enthusiasm for the journey. Axel's courage is a quality that most readers, perhaps, would find understandable, for it isn't ever-present. He experiences many fears and often wants to turn back; he dwells on what is waiting for him at home and worries that he will never make it out alive. However, when the time comes for displays of resolve, Axel marshals his courage. He undertakes taxing endeavors, pushes himself to his limits, and makes himself and his uncle proud. Courage may not be easy to manifest, but it is that difficulty in manifesting it that makes true courage so laudable.
