One of my colleagues called the other day and asked if we still relied on the distinction between intensional and extensional sets (really, intensionally and extensionally defined sets). Yes, even more so now.
An extensional set is one whose members are enumerated. An intensional set is one where individuals gain membership through some sort of rule. The employees in your organization are extensionally defined (e.g., someone puts you in the employee master file and you’re an employee). Cheap hotels within ten miles of the Denver Airport would be an intensionally defined set. (No one is maintaining this specific list, and membership will fluctuate based on rates.)
