A Master Mason spoke to a group of four Entered Apprentices he was teaching: "You've been contemplating the chalk, charcoal and clay with which our ancient brethren served their masters. You understand that these represent certain attitudes or states of mind. What else do you understand?"
The first EA said: "That with charcoal we can ignite the Blazing Star of Truth."
The MM replied: "Your apprenticeship is indeed fervent. How about someone else?"
The second EA said: "That chalk also alludes to the designs of the Master."
The MM replied: "That is some crafty work. Someone else?"
The third EA said: "That we should make our minds like clay, soft and pliable by which to form vessels and molds."
"Almost a masterpiece." replied the MM, who then turned to the last EA and asked, "What can you add?"
The fourth EA said: "No substance. No heat. Not a trace."
The MM smiled and nodded.