diff --git a/doc/sources/guide/lang.rst b/doc/sources/guide/lang.rst
index 5ed607098..96659b3fb 100644
--- a/doc/sources/guide/lang.rst
+++ b/doc/sources/guide/lang.rst
@@ -450,8 +450,13 @@ declaration will have the same kv properties.
 Designing with the Kivy Language
 --------------------------------
 
-The code goes in main.py
-~~~~~~~~~~~~~~~~~~~~~~~~
+One of aims of the Kivy language is to
+`Separate the concerns <https://en.wikipedia.org/wiki/Separation_of_concerns>`_
+of presentation and logic. The presentation (layout) side is addressed by your
+kv file and logic by your py file.
+
+The code goes in py files
+~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Let's start with a little example. First, the Python file named `main.py`: