diff --git a/Nim-for-C-programmers.md b/Nim-for-C-programmers.md
index 0947501..113331e 100644
--- a/Nim-for-C-programmers.md
+++ b/Nim-for-C-programmers.md
@@ -108,7 +108,7 @@ It is possible to implement object-orientation features from other languages (li
 
 ### Structs - Tuples and Objects
 
-Tuples and Objects in Nim are kind of like structs in C, but not really.
+Tuples and Objects in Nim are kind of like structs in C, but not really. Objects, like C structs, use nominal typing. This means that given objects A and B (where B is not a subclass of A), A can not be substituted for B, and B can not be substituted for A, even if they have the same fields. Tuples, on the other hand, use structural typing. If a tuple C contains the same fields as tuple D, they are interchangeable. This is a feature not present in C.
 
 ### Interfacing C and Nim