A commentary on Chen and Campbell (2017): Is there a clear case for addition fact recall?

In their review of Uittenhove, Thevenot and Barrouillet (Cognition, 146, 289-303, 2016), Chen and Campbell (Psychonomic Bulletin & Review, 2017 https://doi.org/10.3758/s13423-017-1328-2 ) concluded that existing evidence supports the conventional wisdom that basic non-zero addition combinations are stored and retrieved as discrete facts and that compacted reconstructive strategies play no role in expert mental addition. One aim of the present commentary is to detail why their evidence supporting these conclusions is not unequivocal. A second aim is to delineate key issues that still need to be addressed to build an accurate model of how basic sums are represented and retrieved.