Walk around a chair or sofa in your home and notice how what you can see changes as you move.

Using a sheet of grid paper, draw some letters of the alphabet so that they appear to be three-dimensional.

The German artist Albrecht Dürer (1471–1528) created an engraving called “St. Jerome in his Cell,” pictured at right. Look in a book or on the web to find a larger reproduction of that engraving. In the engraving, look for lines that intersect in the picture but would be parallel in real life.

Saint Jerome in his Cell Albrecht Durer, 1514