Final answer:
The stage where a couple acknowledges considering marriage is the engagement/commitment stage, as part of the family life cycle's predictable patterns.
Step-by-step explanation:
The stage of family development that begins when a couple acknowledges to themselves and others that they are considering marriage is known as the engagement/commitment stage. This is a part of the family life cycle, a concept used to describe the predictable steps and patterns families experience over time. It's important to note that while there are models like the one proposed by Glick and later expanded by Duvall, these rigid stage theories have been criticized for not accounting for the diversity of modern family arrangements and for making broad generalizations about family life. New models consider a more fluid course of development rather than consecutive stages to better accommodate the variations in family life.