Reason, Observation and Experience — the Holy Trinity of Science — have taught us that happiness is the only good; that the time to be happy is now, and the way to be happy is to make others so. This is enough for us. In this belief we are content to live and die. If by any possibility the existence of a power superior to, and independent of, nature shall be demonstrated, there will then be time enough to kneel. Until then, let us stand erect.

"The Gods" (1876) as published in The Gods and Other Lectures (1879); this was one of his earliest versions of what became known as his "Creed". Some variants: