My personal working definition of philosophy says it is about thinking carefully, thinking clearly, and challenging assumptions. I'd like to discuss a few basic terms and ideas that are commonly confused, and hope to bring clarity.
A good place to start might be a discussion of subjective versus objective truth. What distinguishes one from the other is whether the truth value originates from inside a person’s mind (subjective) or in the world outside a person’s mind (objective). I’ll try to illustrate. If the temperature in a room is 70 degrees, that is an objective truth. It doesn’t matter what anyone thinks or feels about it, it’s 70 degrees, objectively. However, various people in the room may have different personal views about the temperature, based on their metabolisms, what they are wearing, and so on. Some might think that the room is warm, and some might think that the room is cool. These views about the temperature of the room are subjective truth for the individuals, because the origins of the views are in the minds of the subjects. A mistake that is sometimes made is that someone will think that all truth is subjective because it is subjects (people) that are experiencing it. The problem with this is that it commits the logical fallacy of equivocation. Equivocation happens when a word has more than one meaning, and the meanings are confused in usage. In this case the word “subject” is equivocated. The subject, or person, is indeed observing and judging the situation, such as the 70 degree room. But the subject, or person, and subjective, personal truth claims are different things. Subjects can indeed make objective truth claims. It depends upon whether the truth value originates in the subject’s mind (I think it’s warm), or in the world outside the subject’s mind (It’s 70 degrees).
The next step is to distinguish between subjective preference and objective good and evil. If I declare that Rocky Road is the best flavor of ice cream, it probably won’t incite too much controversy. Some people will agree with me, and some will disagree. My liking Rocky Road is recognized as a subjective preference. I can have my favorite, and others can have theirs, or none at all. The source of the preference is in the mind of each person, or subject. On the other hand, there are issues which we intuitively recognize not to be subjective preference issues. Most people, hopefully a vast majority, would say that rape is wrong. Now, is it wrong because people feel that rape is wrong (subjective), or is it wrong because the act of rape is wrong (objective)? Most people would probably say that rape is objectively wrong, regardless of what anyone thinks or feels about it.
If some actions and conditions, like rape, seem to have objective moral value, the question can be asked what makes it objective. Some think Darwinian evolution produces objective morality as natural selection favors characteristics which will enhance survivability. The resultant common perception of certain actions as right or wrong it thought of as objective morality. One problem with this is that Darwinism is purposeless and random. It is entirely possible from a Darwinian perspective that a slight tweak in conditions could have produced an entirely different world where some actions would be given the opposite moral value than we now give them. For example, rape might not be viewed negatively, which may not be far-fetched since we do not usually think of rape as applying to the animal world. If Darwinism could possibly produce such different senses of morality, it does not seem to be adequate to explain objective morality. A second problem with grounding objective morality in Darwinism is that Darwinism is explained as a naturalistic process. This means that all causes are natural, or physical, causes. There are no non-physical causes. Everything that happens boils down to chemical reactions. What we think of as our thoughts and personalities are really only illusion produced by chemical reactions in our brains. These have been passed down through our genes by natural selection for generations until here we are. If this is true, then all of our thoughts, including our moral thoughts, are the result of our DNA interacting with the environment, and we could not do otherwise. What is, simply is, and objective morality is illusion. Darwinist evolution thus seems inadequate to explain objective morality.
Social contract is also offered as grounding for objective morality. People in a society like to live in peace and security. Often they have different views of ultimate reality, but agree to live with a system of rules. Can this agreement, called social contract, ground objective morality? Let’s look at how social contract works. If I don’t want people to take my stuff, and you don’t want people to take your stuff, and everyone else doesn’t want people to take their stuff, then we can organize and agree that if anyone takes anyone’s stuff, they will be punished. That is social contract. But notice something. Where does the process begin? It begins in my personal subjective preference that no one takes my stuff, along with the same subjective preference for everyone else. Even if there is a unanimous agreement that no one should take our stuff, it is still not objective morality, because its origin is subjective preference. Social contract fails to ground objective morality.
What, then, can sufficiently ground objective morality? If humanity’s past and present experience can only produce subjective thoughts and feelings about good and evil, and yet we know intuitively that actions like rape are objectively evil in themselves, it seems that there must be a standard that transcends, or extends beyond human experience, which an action can be compared to in order to call it good or evil. That standard must have a personal, intelligent source to be a sufficient cause for the transcendent moral standard, since a cause has to be adequate to produce its effect. A personal source that can fulfill these conditions is commonly called God.