In this position paper, we enumerate two approaches to the evaluation of visualizations which are associated with two approaches to knowledge formation in science: reductionism, which holds that the understanding of complex phenomena is based on the understanding of simpler components; and holism, which states that complex phenomena have characteristics more than the sum of their parts and must be under- stood as complete, irreducible units.

While we believe that each approach has benefits for evaluating visualizations, we claim that strict adherence to one perspective or the other can make it difficult to generate a full evaluative picture of visualization tools and techniques. We argue for movement between and among these perspectives in order to generate knowledge that is both grounded (i.e. its constituent parts work) and validated (i.e. the whole operates correctly).