There are three kinds of brains. The one understands things unassisted, the other understands things when shown by others, the third understands neither alone nor with the explanations of others.
Lastly, this threefold poetry flows from three great sources - The Bible, Homer, Shakespeare.... The Bible before the Iliad, the Iliad before Shakespeare.
Only one who bursts with enthusiasm do I instruct; Only one who bubbles with excitement do I enlighten. If I hold up one corner and you do not come back to me with the other three, I do not continue the lesson.
The line has magnitude in one way, the plane in two ways, and the solid in three ways, and beyond these there is no other magnitude because the three are all.