For frequency:
* Occasionally: Implies a less frequent occurrence than "sometimes."
* Frequently: Implies a more frequent occurrence than "sometimes."
* Often: Similar to "frequently," but with a slightly less formal tone.
* Rarely: Implies a very infrequent occurrence.
* Seldom: Similar to "rarely," but with a slightly more formal tone.
* Now and then: Informal, similar to "occasionally."
* From time to time: Formal, similar to "occasionally."
* Periodically: Implies a regular occurrence, but not necessarily frequent.
For uncertainty:
* Maybe: Less certain than "sometimes."
* Perhaps: More formal than "maybe," similar to "possibly."
* Possibly: More formal than "perhaps," suggesting a higher chance than "maybe."
* It depends: Emphasizes that the occurrence is conditional.
* Not always: Implies that the occurrence is not consistent.
For specific contexts:
* On occasion: For special or unusual events.
* At times: Similar to "sometimes," but with a stronger emphasis on the variability of the occurrence.
* Every so often: Similar to "occasionally," but with a slightly stronger emphasis on the unpredictability of the occurrence.
* In between: Implies that the occurrence happens within a certain period.
* Occasionally: Implies that the occurrence is not planned but happens unexpectedly.
For emphasis:
* Frequently: To highlight that something happens often.
* Always: To emphasize that something happens consistently.
* Never: To emphasize that something never happens.
The best word to use will depend on the specific situation and the meaning you want to convey. Consider the context, the desired tone, and the level of certainty you want to express.