Forerunner society was based upon a number of hierarchical categories known as rates. Each rate specialized in a particular field of work, and had varying societal function and cultural importance. Rates were divided into several tiers, including forms, guilds and Maniples.
Adolescent Forerunners, known as Manipulars, were not associated with any particular rate. However, upon maturing, each individual Forerunner would be assigned to a rate, mostly in accordance with the rate of their parents. For example, Bornstellar Makes Eternal Lasting was expected to become a Builder like his father.
 List of rates
- Main article: Builder
The Builders were responsible for the construction of a majority of Forerunner architecture. As such, they were responsible for designing and creating most of the Forerunners' megastructures, including the Halo Array and Onyx. The father of Bornstellar was a Builder.
- Main article: Miner
The Miners were the second-highest rate in Forerunner society. They were responsible for obtaining the materials required for the work of the Builders.
- Main article: Lifeworker
The Lifeworkers were the third-highest rate in Forerunner society. They specialized in biology and medicine, especially with the experimentation of various forms of life. It was not uncommon for Lifeworkers to receive their own planets for experimentation. The Librarian was a Lifeworker.
- Main article: Warrior-Servant
The Warrior-Servants were the fourth-highest rate and primary military caste in Forerunner society. They were responsible for, among other things, piloting war sphinxes during the Human-Forerunner wars. The Prometheans were an elite group of Warrior-Servants.
- Main article: Engineer (rate)
The Engineers were the lowest rate in Forerunner society, and were tasked with constructing and maintaining structures and machinery, as well as astroengineering.
- Main article: Juridical
The Juridicals were presumably the rate charged with law enforcement and the judgment of criminals within Forerunner society. Their place in the societal hierarchy is unknown. The Juridicals employed a group of evidence-gathering agents known collectively as the Catalog.
The Theoreticals were a rate that existed over one million years before the Didact was sealed in his Cryptum. Their function and place in Forerunner society are unknown. After one Theoretical named Boundless persisted in studying a certain star in the Spider nebula of Path Kethona despite Warrior orders, she was eventually punished by the Juridicals and sealed within a faulty Cryptum that caused her death. The entire Theoretical rate was then forcibly merged with the Builder rate.