We describe things as being good in two ways. Some things are good because they get us other good things. This is instrumental goodness. Money is a great example of this. Money buys us things we like and is good because it gets us what we want. Other things are good because of what they are. This is called intrinsic goodness. Friendship is a good example of this. We value friendship because it is friendship. No further reason is required. If anything at all is good, then at least one thing is intrinsically good. This leads to the positions of moral pluralism and moral monism.
There is a very simple proof of this claim. Suppose that nothing was intrinsically good. Now suppose that something is good. Since nothing is intrinsically good, that good thing must be instrumentally good. It is only good because some other thing is good. That further thing is good only because some further thing is good as well. This means that there must be an infinite series of things each of which are good only because of the further thing in the series. But that is a problem. Each of these things in the series is only good because of the final thing the series. So if nothing in the series of things is good in itself, then nothing in the series is good at all. Therefore, nothing is good in the series. Since this contradicts the original assumption, we now know that the assumption is false. If something is good, then something is intrinsically good.
There are now two main positions on intrinsic goodness. Either one kind of thing is intrinsically good or more than one are. The position that only one kind of thing is intrinsically good is called moral monism. The position that many things are intrinsically good is called moral pluralism. Generally, moral monists pick one thing such as pleasure, utility, preference satisfaction or the well-being of society and claim that this one thing is what makes everything else good. Moral pluralists do not always have lists. They simply say that many things are good because of what they are. Friendships are good but so is knowledge.
There is only one way to determine which position is better supported by the evidence. We must examine our reasons for claiming that particular things are good. Are friendships good because we both get pleasure from them? Or are they good because they are friendships? If we examine various kinds of goods in this way, it should become obvious which position is right. We can examine our reasons in two ways. First, we could examine the reasons we actually give if we are asked. This way is the least informative. We might be deceiving ourselves, be ignorant of how we actually treat real situations or we might simply have failed to think about the issue in any depth. Second, we could examine the behavior, beliefs and structure of how and why we act the way we do. Do people usually value friendships for their own value or for another value? Their actions will show which position is true.