Voyeurism & Surveillance
The main organizing theme of the film is surveillance, and Harry Caul's relation to it. From the start, the viewer watches the scene in the square through various optical devices and hears bits of conversation as if through a microphone. Harry's entire professional life, and by extension his life itself, is dominated by the act of surveillance and the fear of it. Harry is a voyeur, a spy, who takes his job very seriously, to the extent that he has cleared his own apartment of any threat of surveillance. The stakes of the entire movie are built around the possession of the recorded conversation between Ann and Mark. When he meets Bernie, Bernie celebrates Harry's ability to hear any conversation at any time, and marvels at Harry's subtle insinuations into seemingly un-surveil-able situations. Finally, at the end, Harry is horrified to find that his own apartment has been bugged the whole time, and that Martin Stett has been watching him. The greatest surveillance expert himself is being watched and heard, and it sends him into a maddening spiral of paranoia.
Loneliness and Solitude
Because of his fear of being watched, his sense of duty to his work, and his religion, Harry has largely isolated himself from the world. His apartment seems almost empty, and there are three locks as well as a burglar alarm system and a hidden telephone with a completely private number. The film begins on Harry's birthday, but he doesn't celebrate with any friends, and his co-workers do not know. He brings a bottle of wine over to Amy, his mistress, who seems to be his closest companion, but we soon realize that she knows nothing about him and that their relationship is almost exclusively sexual. She too is isolated from the world, cut off from society, waiting for Harry to arrive in a small dark room. Harry's isolation is what makes him so good at his job—he is committed to getting the job right and he has no distractions—but he also struggles to find a sense of proportion because he is so lonely. As he gets more and more obsessed with the Ann and Mark tapes, he finds himself lonelier, struggling to piece together a puzzle on his own, and ultimately missing the mark. Harry's only solace from his isolation is through his enjoyment of the saxophone, and occasional sexual encounters. Other than that he is cut off from the world.
Confession and Sin
Confession plays a large thematic role in the film. Early on, Harry visits a Catholic confession booth and confesses his sins to a priest, and the viewer realizes that Harry carries a great deal of guilt from a surveillance case that led to murder. Harry is genuinely contrite about his sins, and seeks absolution earnestly. Thus, we see that a major component of his dutifulness and hard work is his relation to guilt and a feeling of repenting for past sins. When Harry lets his guard down with Meredith, he confesses his feelings about Amy, feelings that he would not share with anyone else, but his trust is deeply betrayed when he finds that he has been recorded by Bernie. Then later, in the dream in which he follows Ann through a foggy landscape, Harry confesses a number of childhood experiences to Ann, as though they are sins. Harry carries a great deal of guilt throughout the film, which motivates his every action.
Playing God
The surveillance experts themselves often feel like they have the most control over the world, which lends them a kind of "God complex." At the start of the film, we see Union Square from above—a "God's eye view." Additionally, Harry's ability to hear almost any conversation anywhere gives him a kind of omnipotence. If there is nothing he cannot hear, and no conversation he cannot capture, then he has the ultimate power in most situations. This powerful position is tempered only by Harry's faith in an actual God, and his fear of God's judgment. Bernie is another surveillance expert who believes himself to have an almost divine control of the world. When they have the party in Harry's office, Bernie insinuates that he personally influenced the presidential election through his surveillance work, by tapping phones. His ability to hear anything he wants gives him an inflated sense of power.
Murder
The reason Harry gets so obsessed with the Mark and Ann tapes is that he imagines there to be a darkness underlying their seemingly innocuous conversation. A moment in the conversation that is distorted at first but then becomes clearer upon further listening is the portion of the tapes in which Mark warns Ann, "He'd kill us if he got the chance." Harry Caul becomes obsessed with this one bit of evidence, and worries that the director will murder Ann and Mark, which leads him to follow them to the hotel, where he hears a murder take place. Furthermore, throughout the film, Harry is haunted by the murderous consequences of a past surveillance case in which an innocent family was brutally murdered. Bernie's description of the murder is macabre and disturbing. The subject of murder is explicitly addressed in Harry's dream, when Harry says—half to Ann and half to himself—"I am not afraid of death, but I am afraid of murder."
Corporate Power
The reason that the stakes of Ann and Mark's affair are so high is because Ann is married to a director at a large and powerful corporation, where she and Mark are employed. The director and Martin Stett have a great deal of power, insulated by security, assistants, and corporate bureaucracy. While Harry is a freelance operator, and runs his office out of an open warehouse, the director and Martin are shown in a tall tower, isolated from the less powerful people. Thus, Harry is contrasted with the more powerful director. While Harry is the best surveillance expert in the business and wields a great deal of power because of it, his employers still have the upper hand. At the end, Martin Stett reveals that he is watching and listening to Harry, and we see Harry's sense of agency eclipsed by corporate surveillance.
Family
Harry is completely untethered to anyone. He has no personal friendships, and he keeps his mistress, Amy, completely in the dark about his identity. However, when he speaks to Ann in his dream, he confides about past childhood traumas. In this moment, we can see that Harry's fears and incompatibilities with the world stem from longstanding familial hardships. He rather curiously describes an incident in which his mother left him in a hot bath to go and answer the doorbell and he almost drowned. He felt abandoned by his mother, and this is central to his psychic formation. Harry also tells a story about his punching a friend of his father's in the stomach. The friend died the following year, and Harry feels responsible to this day. We see that many long-standing familial relations are organizing principles for Harry's psyche. Additionally, on the tapes, Ann discusses family ties in relation to the sleeping homeless man on the bench; she tells Mark that whenever she sees a homeless man, she wonders where his family is—"And now, there he is, half-dead on a park bench and where is his mother or his father or his uncles now?"
