To act on (or act upon) is an English phrasal verb that means to take action in response to information, or to exert a physical, chemical, or biological force on something. Depending on whether the subject is a person or a physical force, it applies in two distinct ways:
- Human Action & Decisions: To take specific steps or make decisions based on advice, information, evidence, an impulse, or an order (e.g., “The police acted on a tip from an anonymous caller.”).
- Physical, Chemical, & Biological Forces: To exert an effect, force, or influence on a substance, object, or organism (e.g., “Hydrochloric acid acts on metals to produce hydrogen gas.”).
While act on and act upon mean the exact same thing, act on is far more common in everyday speech, while act upon is slightly more formal and frequently appears in academic, legal, or scientific writing.
Movie and Television Citations
In film and television, screenwriters frequently use “act on” in crime dramas, thrillers, and legal stories during scenes where characters must decide whether to move forward based on unverified intelligence or sudden impulses:
- The Dark Knight (2008): Commissioner Gordon and Harvey Dent discuss handling intelligence against the mob, weighing the risks of moving too quickly without bulletproof evidence: “If we’re going to act on this information, we need to make sure the evidence holds up in court.”
- Minority Report (2002): Federal agents discuss Precrime policy, debating the morality of arresting citizens before they actually carry out a predicted crime: “The Precrime unit doesn’t just predict murder; we act upon that vision before the crime ever takes place.”
- Sherlock Holmes (2009): Holmes explains his investigative process to Watson, emphasizing that one can only make correct deduction from facts: “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, rather than acting on facts.”
- Star Trek: The Next Generation: Captain Picard instructs his bridge officers to execute tactical orders immediately after receiving fresh sensor data: “Number One, we have clear readings. Act on them immediately.”
Sentence Examples
Human Decisions & Information
- “The board meeting ended early so executives could immediately act on the market report.”
- “If you have a strong intuition about a safety hazard, you should act on it right away.”
- “The suspect was arrested after federal agents decided to act upon secret wiretap recordings.”
Physical, Chemical, & Biological Effects
- “Gastric acid acts on food in the stomach to break down proteins during digestion.”
- “In physics, Newton’s first law states that an object will remain at rest unless acted upon by an external force.”
- “Ultraviolet radiation from the sun acts on the skin to produce Vitamin D, but excessive exposure can cause severe damage.”
More Phrasal Verbs with Act
- Act Up: To misbehave, malfunction, or become painfully active.
- Act Out: To express deeper emotional distress or unstated needs through disruptive behavior (unlike “acting up,” which refers to routine misbehavior), or to physically perform a story or role.
- Act Up To: To equal, match, or live up to a standard or expectation.
- Act For: To represent someone or act as their legal or official agent.