Excerpts from: SecularHumanism.org
Secular humanism is comprehensive, touching every aspect of life including issues of values, meaning, and identity. Thus it is broader than atheism, which concerns only the nonexistence of god or the supernatural. Important as that may be, there’s a lot more to life … and secular humanism addresses it.
Secular humanism is philosophically naturalistic. It holds that nature (the world of everyday physical experience) is all there is, and that reliable knowledge is best obtained when we query nature using the scientific method. Naturalism asserts that supernatural entities like God do not exist, and warns us that knowledge gained without appeal to the natural world and without impartial review by multiple observers is unreliable.
Secular humanism provides a cosmic outlook—a world-view in the broadest sense, grounding our lives in the context of our universe and relying on methods demonstrated by science. Secular humanists see themselves as undesigned, unintended beings who arose through evolution, possessing unique attributes of self-awareness and moral agency.
Secular humanists hold that ethics is consequential to be judged by results. This is in contrast to so-called command ethics, in which right and wrong are defined in advance and attributed to divine authority. “No god will save us,” declared Humanist Manifesto II (1973), “we must save ourselves.” Secular humanists seek to develop and improve their ethical principles by examining the results they yield in the lives of real men and women.