Graphs as Tools for Scientific Reasoning

It is now widely recognized that higher-order cognitive ac-tivities such as scientific reasoning are significantly facil-itated by the competent use of visual representations, as there are graphs and diagrams (e.g., Boulter, 2000; Roth & McGinn, 1998). These tools are commonly employed to display relationships between variables; moreover, they can serve as reasoning tools as the inferences drawn from represented information allow the user to derive new con-ceptual insights. For instance, in a coordinate system two variables are represented on the axes and their relation-ship may be displayed by a line graph. The slope of this graph then may represent proportional concepts such as speed, density, or the degree of concentration of different mixtures of liquids. Reasoning about the relationship be-tween the variables displayed in the coordinate syste