Every system of reasoning needs a starting point that isn't derived from something else. In geometry those are axioms. Universal Humanism's foundational axiom is Preserve Life.

Why this axiom?

Preserve Life isn't an arbitrary preference picked from a menu of values. It emerges from the human condition itself. Every person reading this is alive; every value, plan or argument anyone has ever held required a living being to hold it. Life is the precondition of everything else that matters. An ethics that doesn't protect it undermines the very thing that makes ethics possible.

It is also declarative: it is stated as a commitment, "Preserve Life!", and acted on, not merely discovered at the end of a chain of logic. That's why UH treats it as non-negotiable. It isn't put up for a vote, and it can't be traded away as one variable among many.

Good measured by consequence

UH measures good and bad by consequences, with Preserve Life as the standard. An action is good to the degree it preserves life, and bad to the degree it destroys life or causes suffering. Avoiding the destruction of life is not a quantity to be balanced against convenience or profit.

"Reasonably" and intent

The working form is to reasonably preserve life. Nobody can guarantee every outcome, so UH also looks at intent. Two people can produce the same bad outcome: one by accident while trying to help, one on purpose. They are not morally the same. Law already recognizes this with the idea of intent (mens rea): manslaughter and murder can end the same way, but they are different acts.