This paper aims to clarify some aspects of the discussion between "emergists" and "exergists". First, we address the problem of the differences between energy-based emergy and exergy-based emergy: we show that the two are proportional, having the exergetic equivalent of solar energy as scale factor. In the second part, we show that emergy and transformity can be written as a function of exergy alone, in particular of "partial" efficiencies of the processes involved in a production system, from solar energy to the final product. (C) 2006 Elsevier Ltd. All rights reserved.