Able, capable, competent and qualified all mean having power or fitness for work.
Able suggests ability above the average as revealed in actual performance.
- The older child should be able to prepare a simple meal.
Capable stresses the having of qualities fitting one for work but does not imply outstanding ability.
- He’s quite capable of lying to get out of trouble.
Competent and qualified imply having the experience or training for adequate performance.
- Make sure the firm is competent to carry out the work.
- She’s extremely well qualified for the job.