An important aspect of higher education is to educate students who can manage complex relationships and solve complex problems. Teachers need to be able to evaluate course content with regard to complexity, as well as evaluate students' ability to assimilate complex content and express it in the form of a learning outcome. One model for evaluating complexity is the Structure of Observed Learning Outcomes (SOLO) taxonomy. The aim of this analysis is to address the limitations of the SOLO taxonomy in detecting the more subtle differences of the learning outcomes and to clarify the concept of learning modes. This is done by analysing the SOLO taxonomy by means of the model of hierarchical complexity (MHC). The two models are compared by examining their respective theoretical background, the definitions and descriptions of the stages of each model, as well as through evaluating examples illustrating the SOLO levels using MHC. The two models can be viewed as compatible, with MHC also being able to put the SOLO taxonomy in an adult development context, thereby emphasising the importance of developing the students' access to complex thinking.