The moment a percept appears in my field of observation, thinking also becomes active through me. An element of my thought system, a definite intuition, a concept, connects itself with the percept. Then, when the percept disappears from my field of vision, what remains? My intuition, with the reference to the particular percept which it acquired in the moment of perceiving. The degree of vividness with which I can subsequently recall this reference depends on the manner in which my mental and bodily organism is working. A mental picture is nothing but an intuition related to a particular percept; it is a concept that was once connected with a certain percept, and which retains the reference to this percept. My concept of a lion is not formed out of my percepts of lions; but my mental picture of a lion is very definitely formed according to a percept. I can convey the concept of a lion to someone who has never seen a lion. I cannot convey to him a vivid mental picture without the help of his own perception.