"When he (Thomas Aquinas) wants to represent the activity of our reason in knowledge, he takes the image of the flight of birds and says: there is the bird that flies in a rotating, circular way, or the flight that goes forward and backward or the flight that goes from top to bottom, from bottom to top. Circular motion is contemplative motion, motion that goes forward is from cause to effect, backward is from effect to cause, from top to bottom is deduction, from bottom to top is induction. Remembering the flight of birds recalls all the formalities of cognitive activity."