General Ability:
* Capable of: This is a direct synonym for "able to."
* Can: This is the most common alternative and often the most concise.
* Has the capacity to: Emphasizes potential rather than current state.
* Is competent to: Highlights skill and expertise.
* Possesses the ability to: Formal and emphasizes having a specific ability.
Physical Ability:
* Strong enough to: Emphasizes physical strength.
* Healthy enough to: Highlights good health as a factor.
* Fit enough to: Focuses on physical condition.
Mental Ability:
* Intelligent enough to: Emphasizes cognitive ability.
* Smart enough to: More informal than "intelligent."
* Knowledgeable enough to: Highlights knowledge and understanding.
* Skilled enough to: Focuses on a specific talent or expertise.
Circumstantial Ability:
* Allowed to: Highlights permission or authorization.
* Permitted to: Similar to "allowed to," but slightly more formal.
* In a position to: Focuses on opportunity or resources.
* Free to: Emphasizes the absence of constraints.
Emotional Ability:
* Brave enough to: Highlights courage.
* Confident enough to: Emphasizes self-assurance.
* Willing to: Indicates a positive inclination.
The best choice will depend on the specific context and the desired tone of your writing.