Emotional truth
The silliness or seriousness of a scene stands apart from its emotional truth.
Finally a good way of expressing something that I always struggled with in the past.
When focusing on truth in scenes, we tend to go realistic. We stay close to ourselves and explore situations close to our everyday life. Hence we reach 'serious' scenes.
But taking our work seriously (i.e. playing truthfully) doesn't at all need to mean that we have to play serious characters in serious situations. Be silly! Let improv be like dreams, not fiction!