The logic by which the sound flow is apparently born out of the narrative situation itself.  It is a mode of connecting images and sounds that appears to follow a flexible organic process of development, variation, and growth, born out of the narrative situation itself and the feelings it inspires.  

Internal logic tends toward continuous and progressive modifications in the sonic flow, and makes use of sudden breaks only when the narrative so requires.  

Films like Ophuls's Earrings of Madame de, Fellini's La Dolce Vita, or Randa Haines's Children of a Lesser God adopt internal logic.  

The sound swells, dies, reappears, diminishes, or grows as if cued by the characters' feelings, perceptions, or behaviors. 
  

External logic 

The logic by which the flow of sound includes effects of discontinuity as nondiegetic interventions.  

External logic brings out effects of discontinue and rupture to the represented content for example: 

• Editing that disrupts the continuity of an image or a sound
• Sudden changes of tempo
• Breaks

The modern action-adventure film engages external logic quite often to reinforce the tension of the action. Not uncommon is an unexpected double break in the audiovisual flow - a synchronous cut in both sound and image track. 

To Film Sound Theory