What is the difference between agglomerative and divisive hierarchical methods?

Divisive clustering is more commonly used in applications of marketing research.

Hierarchical methods can be always agglomerative.

In divisive clustering, objects are then grouped into bigger and bigger clusters until all objects are part of a single cluster.

Agglomerative clustering starts with each object making up its own cluster. In contrast, divisive clustering starts with all objects being part of a single cluster, and smaller and smaller clusters are then formed until all objects make up their own cluster.