diff --git a/Elements-and-observables.md b/Elements-and-observables.md
index 3d46ab3..7ab2dbd 100644
--- a/Elements-and-observables.md
+++ b/Elements-and-observables.md
@@ -7,7 +7,8 @@ Elements don't interact directly with each other, and constraints don't interact
 Elements | Observables
 ---|---
 Naturally seen as geometric objects | Naturally seen as quantities
-No notion of valence; can interact with any number of constraints | Many important observables have fixed valence
+It always makes sense to ask whether a point lies on an element | It rarely makes sense to ask whether a point lies on an observable
+No notion of valence; can interact with any number of constraints | A valence can be usefully and naturally assigned to many key observables
 An assembly consisting entirely of elements seems meaningful and potentially useful | An assembly consisting entirely of observables seems hard to interpret
 
 ***To do:** Expand and clarify list of contrasts.*