Dialogue is action when it contains the possibility of change. A crucial (and sometimes difficult) distinction to make is between speech that is mere discussion or debate and speech that is drama or action. If in doubt, ask yourself: Can this conversation between characters really change anything? When two characters have made up their minds and know each other's positions on some political or philosophical matter, for instance, they may argue with splendid eloquence but there will be no discovery and nothing to decide, and therefore no opportunity for change. No matter how significant their topic, we are likely to find them wooden and uninteresting. … In order to engage us emotionally in a disagreement, the characters must have an emotional stake in the outcome; we need to feel that, even if it's unlikely they will change their minds, they might change their lives.

Janet Burroway, Writing Fiction, Tenth Edit…, loc. 188