General words:
* Cause: This is the most general term. It describes something that produces an effect.
* Factor: A factor is something that contributes to a result, but may not be the sole cause.
* Influence: This implies a more indirect or subtle effect on a result.
* Catalyst: A catalyst is something that speeds up or initiates a process, leading to a result.
* Agent: An agent is a person or thing that acts or produces a result.
* Instrument: This is a tool or means used to achieve a result.
* Mechanism: A mechanism is a process or system that produces a result.
* Trigger: A trigger is something that initiates or sets off an event that leads to a result.
More specific words:
* Reason: This refers to the specific explanation for a result.
* Motivation: This is the force that compels someone to act and achieve a result.
* Stimulus: This is something that excites or activates a response, leading to a result.
* Driver: A driver is a key factor that pushes something towards a result.
* Precursor: This is something that comes before and contributes to a result.
* Determinant: A determinant is a factor that firmly establishes a result.
Examples:
* Cause: The cause of the accident was a faulty brake system.
* Factor: Lack of sleep was a major factor in the driver's fatigue.
* Influence: Her encouragement had a great influence on his success.
* Catalyst: The new policy was a catalyst for increased productivity.
* Agent: The detective was the agent responsible for solving the crime.
* Instrument: The hammer was the instrument used to build the house.
* Mechanism: The body's natural mechanism helps fight infection.
* Trigger: The loud noise triggered a panic attack.
* Reason: The reason for his absence was illness.
* Motivation: Her desire to succeed was her primary motivation.
* Stimulus: The bright light acted as a stimulus, causing the pupil to contract.
* Driver: Economic growth was the key driver of the company's expansion.
* Precursor: The earthquake was a precursor to the tsunami.
* Determinant: Genetics is a major determinant of a person's height.
The specific word you choose will depend on the context and the nuance you want to convey.