I am certain about some of my moral ideas: genocide is definitely and unequivocally wrong. Some other moral ideas seem equally important, and I would be loath to abandon them, but I feel uncertain or equivocal about them. They capture moral truths, yet they are not fully or certainly right.
Some of my moral ideas are alive in me, informing and guiding the rest of my thoughts and my actual behavior. Other ideas are theoretical or inert: I assent to them but they don’t influence my mind or my actions. Yet (once again) I would be loath to abandon them because they may capture truths that should bind me in new circumstances. For example, if a tyrant arose, I hope I would recall my latent objections to tyranny.
Some of my moral ideas are very general; for instance, Do unto others as you would have them do unto yourself. And some are very particular: make sure that we honor our own organization’s mission statement. My particular ideas do not seem to be mere applications of my general principles, nor are my principles mere abstractions from the particulars. They are different and not fully connected. Again, I would not want to do without any of them.
You could think of these as three dimensions; that would create a space of moral reasons. Each idea can then be placed at a point in the space. I believe that we (because of the kinds of creatures we are) need the full expanse.
Alexis de Tocqueville once remarked that God “stands in no need of general ideas” because He “does not regard the human race collectively. He surveys at one glance and severally all the beings of whom mankind is composed; and he discerns in each man the resemblances that assimilate him to all his fellows, and the differences that distinguish him from them.” Thus God would need no abstractions. God would also have the capacity to act on all of His moral principles, all of the time. He would be fully certain about each of them; and they would all be mutually consistent.
The same is not true for us. Although influential philosophers typically hold subtle and complex views about moral certainty, generality, and the application of moral ideas, I am not sure that we explore–or value, or teach our students to consider–enough of the moral space. We tend to assume that we’d be better off if all our moral ideas could be certain, general, and directly applicable to a broad range of issues and actions. We imagine that the ideal moral agent would fully assent to something resembling a Categorical Imperative (even if not the Kantian version) that would link straightforwardly to the rest of her or his ideas and actions. Nothing like a spiritual exercise (processes for making ideas live in the soul) need intervene between the principles and their application.
The simple view also encourages us to clean things up, getting rid of the ideas that seem partly good and partly bad, or mostly true but not perfectly so, or good under limited circumstances but liable to switch their meanings in different contexts. But the cleanup just deletes some of the the rich experience stored in the full space of our moral reasons.