The Monolith
As with many elements of the film, the iconic monolith has been subject to countless interpretations, including religious, alchemical, historical, and evolutionary. To some extent, the very way in which it appears and is presented allows the viewer to project onto it all manner of ideas relating to the film. The Monolith in the movie seems to represent and even trigger epic transitions in the history of human evolution, evolution of man from ape-like beings to beyond infinity, hence the odyssey of mankind.
Vincent LoBrutto's biography of Kubrick notes that for many, Clarke's novel is the key to understanding the monolith. Similarly, Geduld observes that "the monolith ...has a very simple explanation in Clarke's novel", though she later asserts that even the novel doesn't fully explain the ending.
Rolling Stone reviewer Bob McClay sees the film as a four-movement symphony, its story told with "deliberate realism". Carolyn Geduld believes that what "structurally unites all four episodes of the film" is the monolith, the film's largest and most unresolvable enigma. Each time the monolith is shown, man transcends to a different level of cognition, thus linking the primeval, futuristic and mystic segments of the film: McClay's Rolling Stone review notes a parallelism between the monolith's first appearance in which tool usage is imparted to the apes (thus 'beginning' mankind) and the completion of "another evolution" in the fourth and final encounter with the monolith. In a similar vein, Tim Dirks ends his synopsis saying "The cyclical evolution from ape to man to spaceman to angel-starchild-superman is complete".
The monolith appears four times in 2001: on the African Savannah, on the moon, in space orbiting Jupiter, and near Bowman's bed before his transformation. After the first encounter with the monolith, we see the leader of the apes have a quick flashback to the monolith after which he picks up a bone and uses it to smash other bones. Its usage as a weapon enables his tribe to defeat the other tribe of apes occupying the water hole who do not use bones as tools. After this victory, the ape-leader throws his bone into the air, after which the scene shifts to an orbiting satellite four million years later, implying that the discovery of the bone as tool inaugurated human evolution.
The first and second encounters of humanity with the monolith have visual elements in common; both apes, and later astronauts, touch the monolith gingerly with their hands, and both sequences conclude with near-identical images of the sun appearing directly over the monolith (the first with a crescent moon adjacent to it in the sky, the second with a near-identical crescent Earth in the same position), both echoing the sun-earth-moon alignment seen at the very beginning of the film. The second encounter also suggests the triggering of the monolith's radio signal to Jupiter by the presence of humans, echoing the premise of Clarke's source story The Sentinel.
In the most literal narrative sense, as found in the concurrently written novel, the Monolith is a tool, an artifact of an alien civilization. It comes in many sizes and appears in many places, always in the purpose of advancing intelligent life. Arthur C. Clarke has referred to it as "the alien Swiss Army Knife"; or as Heywood Floyd speculates in 2010, "an emissary for an intelligence beyond ours. A shape of some kind for something that has no shape."
The fact that the first tool used by the protohumans is a weapon to commit murder is only one of the challenging evolutionary and philosophic questions posed by the film. The tool's link to the present day is made by the famous graphic match from the bone/tool flying into the air, to a satellite orbiting the earth, which may or may not be a weapon. At the time of the movie's making, the space race was in full swing, and the use of space and technology for war and destruction was seen as a great challenge of the future.
But the use of tools also allowed mankind to survive and flourish over the next 4 million years, at which point the monolith makes its second appearance, this time on the Moon. Upon excavation, after remaining buried beneath the lunar surface for 4 million years, the monolith is examined by humans for the first time, and it emits a powerful radio signal—the target of which becomes Discovery One's mission.
In reading Clarke, or Kubrick's comments, this is the most straightforward of the monolith's appearances. It is "calling home" to say, in effect, "they're here!" Some species visited long ago has not only evolved intelligence, but intelligence sufficient to achieve space travel. Humanity has left its cradle, and is ready for the next step. This is the point of connection with Clarke's earlier short story, The Sentinel, originally cited as the basis for the entire film.
The third time we see a monolith marks the beginning of the film's most cryptic and psychedelic sequence, interpretations of the last two monolith appearances are as varied as the film's viewers. Is it a "star gate," some giant cosmic router or transporter? Are all of these visions happening inside Bowman's mind? And why does he wind up in some cosmic hotel suite at the end of it?
According to Michael Hollister in his book Hollyworld, the path beyond the infinite is introduced by the vertical alignment of planets and moons with a perpendicular monolith forming a cross, as if the astronaut is about to become a new savior. Bowman lives out his years alone in a neoclassical room, brightly lit from underneath, that evokes the Age of Enlightenment, decorated with classical art.
As Bowman's life quickly passes in this neoclassical room, the monolith makes its final appearance: standing at the foot of his bed as he approaches death. He raises a finger toward the monolith, a gesture that alludes to the Michelangelo painting of The Creation of Adam, with the monolith representing God.
The monolith is the subject of the film's final line of dialogue (spoken at the end of the "Jupiter Mission" segment): "Its origin and purpose still a total mystery". Reviewers McClay and Roger Ebert have noted that the monolith is the main element of mystery in the film, Ebert writing of "The shock of the monolith's straight edges and square corners among the weathered rocks", and describing the apes warily circling it as prefiguring man reaching "for the stars". Patrick Webster suggests the final line relates to how the film should be approached as a whole, noting "The line appends not merely to the discovery of the monolith on the moon, but to our understanding of the film in the light of the ultimate questions it raises about the mystery of the universe."
Read more about this topic: Interpretations Of 2001: A Space Odyssey