Constant, consistent, and persistent can all describe something happening over time. The difference is what you want to emphasize: frequency, a steady pattern, or continuing despite difficulty.
Constant often means happening all the time or very frequently. The constant interruptions made it hard to study. In everyday speech, this does not always mean there were literally no breaks. It can also mean staying unchanged: The water temperature remained constant throughout the test. Here, the focus is on a fixed value.
Consistent means following the same pattern or maintaining a similar standard over time. Her work is consistent: every report is clear and accurate. It does not mean working without stopping. Someone who studies for twenty minutes every evening has a consistent routine, even though they take long breaks between sessions.
Persistent often describes someone who keeps trying despite difficulty or refusal. The persistent student kept practicing until she could solve the problem. It can also describe something that continues and is difficult to stop or remove: A persistent cough kept him awake. This use often refers to an unwanted problem.
- Frequency: Constant messages arrive very often.
- Pattern: Consistent messages arrive at predictable times.
- Difficulty stopping: Persistent messages keep arriving despite requests to stop.
These meanings can overlap. Choose the word that highlights the feature most important to your sentence.