The number of people who don't subscribe to an organized religion has been on the rise in the U.S. since 2007. The Pew Research Center refers to this group as "religious nones," but the people who make up its membership identify themselves in slightly different terms. Quite a few of the "nones" identify as atheists or agnostics. Neither of these is considered a religious affiliation, though they are nevertheless very different.
Nick Fish, national program director of American Atheists, tells Refinery29 that atheism is about as "none" as you can get in terms of belief. "Atheism itself is exactly one thing: a lack of a belief in gods," he says, adding that identifying as an atheist doesn't mean you deny anyone else's beliefs. Rather, atheists are united in their lack of belief and nothing else.
Where an atheist has zero belief in god, an agnostic remains open to the idea of a god, but doesn't worship one in particular. Simultaneously open and skeptical, an agnostic's beliefs are informed by their own experiences.
Agnosticism is often considered a form of humanism, or the worldview that spirituality can be derived from rational, scientific, and moral thought (as opposed to anything divine). While some humanists decisively do or do not believe in a god, an agnostic approach to god is in keeping with humanism because it dictates that it is impossible to prove or disprove the existence of god through science alone.
Before we get too far into the philosophical weeds, a reminder: Atheism and agnosticism are not opposing belief systems. As Fish puts it, "Atheism speaks to what you believe. Agnosticism speaks to what you know or what you think is knowable."
Luckily, there is no authority figure looking over your shoulder, checking your spiritual work, so to speak. A major part of choosing not to follow an organized religion is that how you describe your beliefs is totally up to you. So, if you believe your worldview most closely aligns with atheism, agnosticism, or if you'd rather be known simply as a "none," you're free to make that a part of your spiritual identity.