 Note that it seems natural to identify these two extensions given that all and only the objects that fall under the first concept fall under the second. Those readers already familiar with the \(\lambda\)-calculus should remember that \(\epsilon[\lambda x~\phi]\) denotes an object, that \([\lambda x~\phi]\) denotes a concept, and that Frege rigorously distinguished objects and concepts and supposed them to constitute mutually exclusive domains.