This document discusses various reasoning requirements for developing and using biomedical ontologies. It describes techniques like using classification to complete modeling, asking modelers to make minimal changes and letting reasoners handle complex tasks, checking ontologies against instances, finding gaps by querying experts, discovering new relations from data, and performing complex queries across linked ontologies using part-whole relations. Reasoning can support ontology development, classification, changes, error finding, gap identification, and more. However, some tasks like large-scale ontology comparison and open-ended path queries may not be feasible.