by heart

1. When you learn something by heart, you learn it so well that you can repeat it from memory quickly and without thinking about it.
   The fool learned the whole telephone book by heart.

   The teacher is a poet and he forces his students to learn his poems by heart.

   I learned my girlfriend’s phone number by heart.
2. When you know something by heart, you can repeat it from memory quickly and without thinking about it.
   The fool knows many historical dates by heart but he does not understand history at all.

   My son goes to school and he knows many poems by heart.

   The philosopher was delighted when he met the fool because the fool knew by heart his thick book on philosophy.