Dead Poets Society explores many themes, including rebellion, coming of age, and individuality. However, the most significant theme of Dead Poets Society is captured in the phrase "carpe diem," which literally translates to "seize the day." This theme arguably overlaps with the other themes in several ways, and thus, I think, it could be called the main theme. This theme is explored throughout the film in many layers and characters—most notably in that of Neil. Another way of looking at this theme is to think of it as an expression of the tension between life and death. The monotony that the "four pillars" of Welton Academy offer is to be understood in direct contrast to the celebrated nature of the classroom space that Professor John Keating operates in.

This theme becomes clear with the death of Neil, a student who wants to pursue acting but is forced into academics by his father. His death is the metaphor of life and death taken to its extreme. The only way that Neil could "seize the day" was by pulling the trigger, because he knew that his father would never let him out of academics if he were to continue to live. Ironically, by choosing to die, Neil sought to escape the monotony of the life his father sought for him.

One of the most prominent themes of this film is revealed on John Keating's (Robin Williams) first day of teaching. He brings his class to the hallway to gaze on the portraits of several dead poets and whispers "Carpe Diem" which is Latin for "seize the day."

This concept is in direct contrast to the opening scene of the film, in which the "four pillars" of the school are recited in an opening assembly: tradition, honor, discipline, excellence. Essentially, the teaching method at Welton Academy has always been one of conformity, recitation, and acceptance of authority. Keating introduces his students to a new way of thinking, which is just that, thinking. He teaches the boys to think for themselves. He teaches them to seize opportunities ("Gather ye rosebuds while ye may...") and to consider the personal consequences over the consequences implemented by authority.

As a result, Keating's students begin to make choices that go beyond the scope of their once very robotic lives. They experience both the positive and the negative consequences of their choices, but most importantly, they learn, grow, and mature.