The quality or state of being able; power to perform, whether physical, moral, intellectual, conventional, or legal; capacity; skill or competence in doing; sufficiency of strength, skill, resources, etc.; in the plural, faculty, talent. Then the disciples, every man according to his ability, determined to send relief unto the brethren. (acts xi. 29) Natural abilities are like natural plants, that need pruning by study. (Bacon) The public men of England, with much of a peculiar kind of ability. (Macaulay)
ability and capacity come into comparison when applied to the higher intellectual powers. Ability has reference to the active exercise of our faculties. It implies not only native vigor of mind, but that ease and promptitude of execution which arise from mental training. Thus, we speak of the ability with which a book is written, an argument maintained, a negotiation carried on, etc. It always something to be done, and the power of doing it.
capacity has reference to the receptive powers. In its higher exercises it supposes great quickness of apprehension and breadth of intellect, with an uncommon aptitude for acquiring and retaining knowledge. Hence it carries with it the idea of resources and undeveloped power.