One possibility: we can see a connection between morality and certain empirical facts—for example, if we believe that more moral societies will be more stable, we might think that we can see moral progress in the form of changes that are brought about by previous morally related instability. That’s not very clear—but a much clearer and more sophisticated variant on that idea can perhaps be seen in an old paper by Joshua Cohen, “The Arc of the Moral Universe” (google scholar will get it, and definitely read it, because a) it’s brilliant, and b) I’m not representing it very well).
Or we might think that some of our morally relevant behaviors are consistently dependent on empirical facts, in which we might progress in finding out. For example, we might have always thought that beings who are as intelligent as we are and have as complex social and emotional lives as do we deserve to be treated as equals. Suppose we think the above at year 1 and year 500, but at year 500, we discover that some group of entities X (which could include fellow humans, as with the slaves, or other species) is as intelligent, etc., and act accordingly. Then it seems like we’ve made clearly directional moral progress—we’ve learned to more accurately make the empirical judgments about which our unchanged moral judgment depends.
One possibility: we can see a connection between morality and certain empirical facts—for example, if we believe that more moral societies will be more stable, we might think that we can see moral progress in the form of changes that are brought about by previous morally related instability. That’s not very clear—but a much clearer and more sophisticated variant on that idea can perhaps be seen in an old paper by Joshua Cohen, “The Arc of the Moral Universe” (google scholar will get it, and definitely read it, because a) it’s brilliant, and b) I’m not representing it very well).
Or we might think that some of our morally relevant behaviors are consistently dependent on empirical facts, in which we might progress in finding out. For example, we might have always thought that beings who are as intelligent as we are and have as complex social and emotional lives as do we deserve to be treated as equals. Suppose we think the above at year 1 and year 500, but at year 500, we discover that some group of entities X (which could include fellow humans, as with the slaves, or other species) is as intelligent, etc., and act accordingly. Then it seems like we’ve made clearly directional moral progress—we’ve learned to more accurately make the empirical judgments about which our unchanged moral judgment depends.