One characteristic that requires a better description in the transfer literature is far transfer. The distance of transfer is often a very subjective matter depending on how similar the base and target are proposed to be. Four levels at which relations of similarity can be made are outlined in an effort to better describe judgments on transfer distance. Each increased level corresponds to a more distant form of transfer with far transfer occurring when judgments at the highest level of similarity are used. This highest level of similarity is called thematic similarity. Similarity at the thematic level is distinguished from the previous three levels in that judgments at this level are prefigurative rather than structural. Far transfer is formally defined to occur when themes are the primary source of similarity between a target and base and when the structure of the problem is ill-defined from the actors perspective.