With knowledge of the internal stability of a closed-loop system with an unknown plant Panda known controller C-1, the stability and performance of another closed-loop system with the same P and a known candidate controller C-2 are divined without constructing the (P, C-2) loop. This is performed through nonparametric identification of the frequency response functions of P or other transfer functions, based on a limited amount of signal data collected from experiments on the internally stable (P, C-1) closed-loop system excited by designed reference signals and corrupted by disturbances. An error analysis is provided and conditions for the reliable assessment of stability and performance are characterized. Linkages with the works of others in controller validation, certification, and unfalsification are studied and connections to system identification for control are explored, notably in the treatment of deliberate experiments and assumptions in moving from unfalsification to divination. (C) 2012 Elsevier Ltd. All rights reserved.