I think that you can use "capacity" to replace "ability", For example I have the ability to make a change. I have the capacity to make a change. These 2 sentences means more or less the same but you cant use "ability" to replace "capacity" Like what Jit-Keong said Example An airplane has the capacity of 500 passengers. In this sentence you can never replace "capacity" with the word "ability", because that would not make any sense "capacity" and "ability" can both be referred to as having the ability or capability to do something However capacity has another meaning which some English words also have. It also refers to how much a thing can hold example A jar has a capacity of 100 ml. A box has a capacity of 10 chocolates and etc I hope this helps ^^

Well, imagine that you are a kettle or water heater. :P Your capacity will be the amount of water your can hold. It could be 1 litre or 2 litre etc. Your ability will be the fact that you can make the water boil; you can dispense the water by pouring it out through the spout etc.

er...capicity?i think you mean the"capacity"^^ ability means that sb. can do sth. in paractice,if sb. can learn sth. quickly,then we can say he has the capacity to learn ...capacity emphasise the ability of acceptance. show you a sentence:he may have great capacity for acquiring knowledge,and yet not process ability to teach.

what cowboy said =)

Capacity is the cabability to perform or produce while ability the quality of being able to perform; a quality that permits or facilitates achievement or accomplishment and possession of the qualities (especially mental qualities) required to do something or get something done. cowboy...