But I mentioned earlier that we can know what objective morals are and what they entail IE (morals that are right and wrong independent of humans). We also can know objective morals through our intuitions. We can make predictions about our intuitive morality and then seek to find this and measure it to see if it matches. Science uses the same method in making assumptions and then seeking to verify them.
But also there are other ways people can know objective morality such as through human wellbeing and hurting people. Many who support objective morality use this method. In fact because we know that there have to be certain moral truths because humans know and live this way there is a movement to come up with ways to support objective morality that doesn't involve using a transcendent moral lawgiver. IE
How Morality Has The Objectivity That Matters—Without God
The thesis of this essay is that morality is not objective in the same the way that statements of empirically verifiable facts are objective, yet morality is objective in the ways that matter: moral judgments are not arbitrary; we can have genuine disagreements about moral issues; people can be mistaken in their moral beliefs, and facts about the world are relevant to and inform our moral judgments.
How Morality Has the Objectivity that Matters—Without God | Free Inquiry
The Moral Landscape by Sam Harris
http://www.youtube.com/watch?v=gqM_NE4Zk2s
The greatest moral challenge of our time? It’s how we think about morality itself
Murder is wrong. This is not just a matter of subjective personal preference, it’s an objective fact.
The greatest moral challenge of our time? It's how we think about morality itself
But even if we disregard all these questions about how we know objective morality is true are irrelevant just the same as how we know God is real. They don't disprove that objective morals are not true. You can never disprove there are no objective morals. But I only have to show that there is one objective moral to support there are objective morals.
But this does not stop people from providing indirect evidence and logical arguments for God and objective morals. In fact, one argument for God is that there are objective morals and with God, there is no moral right and wrong. There are other arguments for God such as the fine-tuning and cosmological argument.
This is the same for objective morals such as the one based on our lived moral experience. Just like we can be justified in believing that our physical world is real based on our lived experience of it we can also be justified to believe that there are objective morals based on our lived experience that people live and act live there are objective morals.
Until a defeater is given that will completely show that our experience of objective morals is completely unreliable we can be justified in our belief about there being objective moral values and duties.