Lardiere's keynote article adverts to a succession of "units of comparison" that have been employed in the study of cross-linguistic differences, including mid-twentieth-century structural patterns, generative grammar's parameters, and (within contemporary Minimalism) features. This commentary expands on the idea of units of cross-linguistic comparison, first by developing Lardiere's observations about recent scholarship and, second, by identifying some earlier reflexes of the notion. I close by suggesting that thinking about "units of comparison" across time prepares us to better appreciate a feature-based conceptualization of L2 acquisition, and its likely trajectory.