The next option in the list was “feelings”. This seems like it would be a popular answer if you asked a lot of people where they thought morality comes from. Probably lots of people believe that morality comes from inside themselves, from how they feel about actions. Someone who holds that view would probably say that their conscience tells them what is morally right and wrong. If an action feels wrong to them, then it is morally impermissible, and if it feels right, then it’s morally permissible.
The moral theory that is based on this view is called Sentimentalism. It’s called that because on this moral theory, morality comes from your sentiments (or feelings). Most sentimentalists like to be a little more specific about the feelings that they use to define moral rightness and wrongness, because saying that some action “makes me feel bad” is a little too vague. Typically sentimentalists will say that the particular sentiment that matters is approval. For a sentimentalist, if you feel a sentiment of approval toward some action, then that action is morally permissible. If you feel a sentiment of disapproval toward the action, then it is impermissible. Using conscience to determine moral permissibility is limited, because usually in order for your conscience to kick in, you actually have to do the action yourself, and then your conscience will make you feel bad about it, or make you feel okay about it. But sentimentalism isn’t that limited. You don’t have to do the action yourself—you don’t even have to witness the action—to figure out whether it is morally good or morally bad. All you need to do is think about it.
The Scottish philosopher David Hume introduced this idea by pointing out that whenever you find an action to be morally good (hume uses the term ‘virtuous’) or morally bad (Hume uses ‘vicious’), the judgment comes from inside you, not from the action itself. He says that moral judgments are like colors or sounds. They are perceptions (feelings) inside the observer.
Take any action allowed to be vicious: Wilful murder, for instance. Examine it in all lights, and see if you can find that matter of fact, or real existence, which you call vice. In which-ever way you take it, you find only certain passions, motives, volitions and thoughts. There is no other matter of fact in the case. The vice entirely escapes you, as long as you consider the object. You never can find it, till you turn your reflection into your own breast, and find a sentiment of disapprobation, which arises in you, towards this action. Here is a matter of fact; but it is the object of feeling, not of reason. It lies in yourself, not in the object. So that when you pronounce any action or character to be vicious, you mean nothing, but that from the constitution of your nature you have a feeling or sentiment of blame from the contemplation of it. Vice and virtue, therefore, may be compared to sounds, colours, heat and cold, which, according to modern philosophy, are not qualities in objects, but perceptions in the mind: And this discovery in morals, like that other in physics, is to be regarded as a considerable advancement of the speculative sciences; though, like that too, it has little or no influence on practice. Nothing can be more real, or concern us more, than our own sentiments of pleasure and uneasiness; and if these be favourable to virtue, and unfavourable to vice, no more can be requisite to the regulation of our conduct and behaviour.
Sentimentalism uses these perceptions, or feelings, or praise and blame to determine what is morally permissible or impermissible. If you consider an action, like for example giving some money to charity, you might feel a sentiment of approval (Hume would say ‘praise’) about it, then the action is permissible. If you consider another action, like stealing candy from a baby, and you feel a sentiment of disapproval (Hume would say ‘blame’) about it, then the action is impermissible. If you consider yet another action, like rescuing a small child from drowning in a shallow pool (one so shallow that there is no danger of drowning yourself), and you feel a sentiment of disapproval about not doing it, then it is obligatory.
So for sentimentalists, all that is necessary is to consider the action in question, and think about whether you approve of doing it (permissible), disapprove of doing it (impermissible), or disapprove of not doing it (obligatory). In this way, sentimentalists are able to determine the moral rightness or wrongness of actions using their feelings.
Of course, there is one glaring problem with sentimentalism. What if someone doesn’t feel the sentiment we would expect? What if they don’t feel disapproval toward the idea of stealing candy from a baby? What if they feel perfectly fine about torture and murder, and don’t have any problem with letting children drown in shallow pools? What if they just don’t feel any way about those things? A sentimentalist can’t just say “that’s fine, if you don’t have any problem with murdering people, then go right ahead.” We’d probably say that person is a sociopath, but that doesn’t solve the problem for sentimentalists. If you’re going to say morality comes from feelings, then you have to hold everyone to the same standard. And anyway, you might not approve or disapprove of things in less extreme cases depending on your mood, and a moral theory that depends on your mood doesn’t seem like a very good system.
So sentimentalists have come up with a solution. They say that it’s not whether you actually feel the sentiment of approval or disapproval, it’s whether the action merits the feeling. “Merits” means something like “deserves”. So if an action merits disapproval, then it is appropriate to feel disapproval. For example, murder merits a feeling of disapproval. Even if you don’t happen to feel disapproval, it would be appropriate to, since murder deserves to be disapproved of. So sentimentalists can now say that whatever actions merit a feeling of disapproval are impermissible, whatever actions merit feelings of approval are permissible, and whatever actions merit feelings of disapproval for not doing are obligatory. Often sentimentalists use the terms ‘praiseworthiness’ (that it is worthy of praise) and ‘blameworthiness’ (that it is worthy of blame).
But now there is a new problem. How do we know if an action is worthy of praise or blame? What if you are one of the people who doesn’t happen to feel the appropriate sentiments? How would you even know? Whose sentiments can you trust? You can’t just say that the majority of people feel a certain sentiment about some action, and that is why the action merits the sentiment, because that would just be relativism!
There is no clear solution to this problem, so we just have to admit that sentimentalism might work sometimes, but is not really as reliable as we’d like our system for determining morality to be.
 Hume, David, A Treatise of Human Nature, Project Gutenberg collection, 2010, Book III, Sec.1, Part 1. http://www.gutenberg.org/files/4705/4705-h/4705-h.htm