The time has come for a basic distinction: ends v purposes.
Yes, in everyday language they are basically the same thing. If we think about them as distinct, however, we uncover an important real distinction in the world. This is a classical distinction (meaning, it has been kicked, scuffed, and otherwise violated by some modern and post-modern philosophers), but it is still respected in some circles; and it is still a wonderful way to approach the world.
Ends are inherent to a thing or an activity. That means they are in the thing or activity by nature. The thing or acitivty is the best that it can be when it is pursuing and, finally, has achieved its end. Ends do not change and cannot be changed by us. We can only discover ends.
For example, the end of the art of medicine is healing. We cannot change the end, healing, without making medicine unrecognizable. If he's not healing, he's not practicing medicine.
Here's an example from another happy activity: the end of philosophy is a true theory (theoria); that is, a true vision (speculum) of the world, of God, of ourselves. To conform our minds to an already-existing truth is the end. Our thinking is the best it can be when it grasps truth. The greater the truth, the more perfect the act of thinking.
Purposes are not ends. Purposes are imposed by human beings upon things. We create purposes.
For example, a tree stump has no real purpose or use for us until we decide, "Ah ha! What a perfect resting place for my tired self!" We impose the purpose--be a seat--upon the otherwise indifferent stump.
Of course, that's morally neutral, and no one gets too many feathers ruffled over you sitting on a stump.
Purposes become sticky, however, when we decide to pervert an end. The medicine example was deliberately chosen. Medicine, in the tradition, has the end healing. When someone imposes a different purpose on it, we all become quite disturbed (or ought to become disturbed). If we suspect a doctor or HMO is in medicine only for money, we sense that there's something out-of-place. The natural end of medicine has been sacrificed for a man-made purpose.
This distinction is dreadfully (and I do mean dreadfully) important for most talk of ethical concerns and the appreciation of contemplation. To know the end of something is to receive a truth about it from outside yourself. To simply impose your own purposes on things means you never really get outside of yourself.
And my self is a rather dull companion.