Why are O and E sometimes attached together, as in “les œufs”?

Question

I asked my French teacher last time, and she said she didn't know, but she will ask. Can anyone give clear and simple reason for this?

Answer 1

The letters O and E became glued together as pronunciation evolved and the letters started to be pronounced as one sound/one syllable instead of two. When the letters are separate, they form 2 sounds. Example:

« coefficient », which will be cut like « co/ef/fi/cient. When the letters are glued together (« œ »), they form a single sound ([e] ou [ɛ]) Examples: “œuf” (= egg).