I like the phrase “good without god(s),” because it reminds us that morality does not come from supernatural sources. But there’s a flip side to that: if we can be good without God, then we can also be evil without the devil, as has been horrifically demonstrated in the Chapel Hill shooting.

The thing is, atheism is just a fact, like the speed of light or the law of gravity. We don’t get any moral impetus from the fact that we obediently accelerate towards the center of the earth at about 32 feet per second squared. Knowing the correct value for the acceleration of gravity may give us a scientific advantage over people who don’t know, or who choose to believe in erroneous values. But that give us no moral advantage.

And it’s the same with atheism. Seeing the absence of the gods, understanding the superstitions and rationalizations that lead people to believe in beings that aren’t there, knowing the history of religion with its triumphs and tragedies—these are all simply observations. They’re not a source of moral guidance or motivation.

I do not believe that atheism, by itself, could or should motivate us to better behavior, any more than the law of gravity does. This doesn’t mean I disagree with Atheism+ or the things PZ Myers is saying about how we ought to respond, as atheists, to moral issues. I heartily agree that, as atheists, we should all be concerned about things like social justice (which, after all, is nothing more than justice as applied to a specific set of injustices). But this additional concern is something more than just atheism. The “plus” in Atheism+ is essentially a set of values that are taken from (or built upon) the humanistic ideals of the Enlightenment, plus what we’ve learned since then.

This “plus” is the difference between atheism and secular humanism. Someone could acknowledge the non-existence of gods and say, “So what?” They’d technically be an atheist, but we can echo their question: so what? The difference between the atheist and the humanist is in how they respond to the absence of gods. Atheism, by itself, does not specify any particular response. Maybe individual atheists realize that this means we are on our own and we make our own justice and morality, according to what works best within the constraints of the laws of nature and our own best interests. If so, they’re humanists as well as atheists. But maybe they don’t care. Maybe they’re unpleasant people who basically revel in the common caricature of the atheist as a dangerous and unpredictable loner. Maybe they’re even psychopaths and murderers. They’re still atheists, just not humanistic atheists.

That’s why I prefer “humanism” as the core set of values that ought to define who we are and the common interest we all share. We’re all humans. We’re humans in a godless world, and it’s up to us to make the best of it. We know that whatever world we build, that’s the world we live in. If we fill the world with violence and vengeance and bullying, then we get to live in fear and constant retribution. If we fill the world with tolerance and liberty and understanding, then we get to be free from fear and ignorance.

The human world is whatever humans make of it, without magic and without deus ex machina to make everything right when we screw up. If we break something, it’s up to us to fix it, or it won’t get fixed. But if we build wisely and well, then we get a better world to live in. That’s our motive. That’s our moral imperative.

Humanism gives us a reason to live better lives and to be civilized and tolerant towards one another. Atheism, not so much. Atheism is about what isn’t. Humanism is about what is.