 The true sentence, “All oaks are trees” becomes false when reversed. So does, “All carrots are vegetables.” Can we say that every true sentence beginning with ‘all’ becomes false when reversed? The children in Harry Stottlemeier’s Discovery initially are tempted to say, yes. But at least as early as the 3rd grade, children easily find exceptions. What about “All tigers are tigers”, many will ask. Others may respond that this is an uninteresting sentence, offering something like “All rabbits are hares,” or “All mothers have children” as alternatives. With relatively little encouragement, they can come up with good definitions of geometric figures and differentiate them from proposed definitions that cannot be reversed. For example, “All squares are rectangles” is true, but it becomes false when reversed. “All squares are rectangles with equal sides,” however, can be reversed.