Both able and capable are used to say that someone can do something.
When you say that someone is able to do something, that they can do it either because of their knowledge or skill or because it is possible for them to do it.
1. Breslow wondered if he would be able to climb over the rail.
2. They must be able to use their profits for new investment.
Note that if you use a past tense, you are saying that someone actually done something.
3. We were able to reduce costs.
When you say that someone is capable of doing somethmg, you mean either that they have the knowledge and skill want or need to, or that they are likely to do it.
4. Workers are perfectly capable of running the organizations whic employ them.
5. She was quite capable of dropping off to sleep.
You can also say that someone is capable of a feeling or an action.
6. I think he’s capable of loyalty and seriousness.
7. Bowman could not believe him capable of murder.
You normally use ‘capable of’ when talking about what something such as a car or machine can do.
8. …water turbines, which are capable of producing more economical electricity.
9. The car was capable of 110 miles per hour.
If you describe someone as able or capable, you mean that they do things well and in an intelligent way. There is little difference between the two words when used in this way.
10. …the able and methodical King Charles V of France.
11. This very able man totally failed to see the possibilities of the telephone.
12. Newborn babies are more capable than was once thought.
13. Well, you certainly have a capable gardener there.