A more general approach to distinguishing between so-called homogeneous vs heterogeneous catalysts has been developed and intrinsically : tested in answering the question "what is the true catalyst in the active hydrogenation system which evolves from cyclohexene, hydrogen, and the discrete, polyoxoanion-supported Ir(I) catalyst precursor (Bu(4)N)(5)Na-3[(1,5-COD)Ir.P2W15Nb3O62]?". The approach developed and utilized consists of four categories of experiments : (i) catalyst isolation and characterization studies, with an emphasis initially,on TEM (transmission electron microscopy); (ii) initial kinetic studies, emphasizing whether or not the isolated catalyst can account for the observed kinetics, especially any induction period seen, and whether pr not the reaction exhibits a +/-10% reproducible rate; (iii) quantitative phenomenological catalyst poisoning and recovery experiments;(iv) additional kinetic and mechanistic studies and chemical tests, all interpreted with strict adherence to the principle that the correct description of the catalyst (i.e., the correct mechanism) will explain all of the data. The present approach has identified a previously unknown type of hybrid homogeneous-heterogeneous, Ir-similar to 190-45.polyoxoanion/BU4N+ catalyst of average composition [Ir(0)(similar to 300) (P4W30Nb6O12316-)(similar to 33)](BU4N)(similar to 300)Na-similar to 233. The discovery of, and ability to distinguish, even an unprecedented hybrid homogeneous-heterogeneous catalyst strongly suggests that the present approach will be more generally applicable to the difficult and often unsolved mechanistic problem of distinguishing catalysis by a discrete, homogeneous metal complex vs that by a soluble metal nanocluster or colloid "heterogeneous" catalyst. Some false starts and incorrect leads in the early stages of this work are discussed, research which illustrates some of the pitfalls to be avoided in attempts to distinguish homogeneous from heterogeneous catalysts. A minimum mechanistic scheme for the catalyst’s evolution, consisting of the autocatalytic generation of the Ir-similar to 190-450 nanoclusters, is shown to account for all of the observed results, including the findings of the rate-enhancing effects of H+, H2O, and acetone impurities that were puzzling in the earlier stages of this work, before the Ir-similar to.190-450 nanocluster catalysts were identified.