How is the creature smart?

The creature laments about the meaning of life. He is pretty introspective musing about everything from the nature of God to Milton's Paradise Lost. Oh yes, he teaches himself to read! He also has a strategy for revenge which is quite clever.

Victor's creature is intelligent and sensitive. He tries to integrate himself into society and to follow human social patterns, but because of the way he looks and acts (he is a creature after all), he feels abandoned and unwanted. These feelings lead him to seek revenge against Victor.