Perspectives seen from different points of view
Plato stated that as things appear, is different from as things are. He found that e.g. perspective (skhnografia - 'scene-painting') and the magic of light and shadow often lead to contradictions or illusions. But according to Plato we are rescued from this confusion of contradictions and illusions by measuring, counting and weighting (Republic, X,602C-3B). Aristotle was less afraid to rely on the human senses (resulting in 'common sense') while observing the appearance of eventities. It's after all the human 'rational sense' that guides the measuring, counting and weighting. Perhaps already these and for sure later philosophers understood that contradictions and illusions can be involved in the processes of measuring, counting and weighting as well.