Shape

83 What Makes Calculating Visual?
because I don’t know how the sides of triangles are divided—remember, there’s no
telling how many lines there are in a shape—or even if sides are parts. And I don’t
have to divide Evans’s shape into constituents either for the identity to apply in the
way I want, to find every triangle. The shape is OK as a drawing, too
When I use the identity, there are sixteen triangles—this is just what I see and can
trace—even though the small triangles and the medium ones have maximal lines that
aren’t maximal lines in the shape. My erasing rule—the one I added to Evans’s
grammar—is
and it produces the results I get if I erase the lines I see by hand. In practical terms, this
is just tracing again. If I apply the rule to the sides of small triangles, the shape disappears.
And when I use it to take away the sides of medium or large triangles, I get
the cross
This is the way it’s supposed to work—seeing and calculating agree perfectly. When I
see a part and change it according to a rule, nothing is hidden to confuse the result.
Whatever distinctions a rule makes, I can see. There may be surprises—there are plenty
to come—but they aren’t conceptual ones caused because I’ve represented shapes with
constituents that I can’t vary after I begin to calculate. There’s no hidden analysis that
determines what I can see and what I can do. Surprises are perceptual. They’re a natural
part of sensible experience. And the rule
—another identity—finds as many Y’s in the shape as you care to see. Seeing is never
disappointed. There’s no part I can see that a rule can’t find. Novelty is always possible.
What you see is what you get.
It may be useful to digress a little to compare Evans’s example for points and for
lines. For points, there are finitely many parts for rules to find, but for lines, there are
indefinitely many parts. This is perfectly clear for Y’s. And it’s fundamentally so for the
rules