A commentary on processing instruction

The commentary takes the form of reflections occasioned by the debate carried out in the various contributions to this volume as also the related presentations and discussions that took place at the Symposium on Processing Instruction at the University of Greenwich in September, 2013. Rather than review each contribution the debate is be placed within a historical perspective and focus is on the changing relationship between two types of professional: a) those who seek to extend our understanding of second language acquisition and b) those whose main aim is to assist language instructors by applying insights from theoretical research and, by so doing, provide their profession with a modern scientific foundation. It is about the relationship between the 'understanders', on the one hand, and the 'helpers' on the other. The interaction between Input Processing Theory (IP)- the theory - and Processing Instruction (PI) - the application - provides an ideal background for such a discussion.