What is the term for someone or something that encourages progress or change?

The appropriate term for someone or something that encourages progress or change is "catalyst." In various contexts, a catalyst refers to an agent that provokes or speeds significant change or action, often in a transformative or impactful way. In scientific terms, a catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent change itself. This idea translates well into social or personal contexts, where a catalyst can be an individual, event, or even an object that inspires or triggers a movement or transformation.

The other terms provided do not capture this meaning. A "stanza" is a specific form of poetic structure that comprises a grouped set of lines, more relevant to the organization of written work rather than the concept of change. An "imperative" relates to commands or requests in grammar, which doesn't suggest encouragement or progress. A "euphemism" is a figure of speech that replaces a harsh or direct term with a softer one; this does not relate to inspiring change directly. Thus, the term "catalyst" stands out as the most fitting choice for encouraging progress or change.