Over the years, two new strands of research have evolved from the phenomenographic research tradition: the first concerns advancement of the variation theory of learning, whilst the second involves development of the learning study approach. In this paper, the conceptual frameworks of phenomenography, variation theory, and learning studies are critically examined, and we revisit the notion of "critical aspects," one of the running threads connecting the three research strands. More specifically, we highlight the notion's relational nature and its relationship with so-called irrelevant aspects. We further argue that we must take care not to lose sight of its connection to the basic tenets of the wider phenomenographic research paradigm to ensure that learning studies make a powerful contribution to education.